# Use cases

This chapter is mainly dedicated to the appearance of the application and a description of the individual paths that the end user will follow depending on the payment method he choosed. Each of the payment method available in Paytool application is described in a separate section. Additionally, every chapter contains diagrams depicting the entire transaction process per payment method.

<p class="callout success">**Tip:** Check it now. Verestro Paytool demo application is available [here.](https://paytool.verestro.dev/demo/)</p>

## Transaction initialization

The first step of the each transaction always takes place in your application. Your application integrated with the Verestro Paytool solution should have exposed option allowing to pay using Paytool available in your application. Your backend should deliver the initial transaction data to the Paytool API to open new transaction session when your payer selects the Paytool as payment option. Our API will return you the transaction identifier and the payer's redirection address. The view of transaction initiatialization from the end user's perspective has been shown below. This view refers to the [Redirect your payer](https://developer.verestro.com/books/paytool/page/overview#bkmrk-redirect-your-payer) integration path:

<table border="0" id="bkmrk-%C2%A0-%C2%A0" style="border-collapse: collapse; width: 100%; height: 29.7969px; border-style: hidden;"><tbody><tr style="height: 29.7969px;"><td style="width: 50%; height: 29.7969px;">[![image-1687851731553.png](https://developer.verestro.com/uploads/images/gallery/2023-06/scaled-1680-/image-1687851731553.png)](https://developer.verestro.com/uploads/images/gallery/2023-06/image-1687851731553.png)

</td><td style="width: 50%; height: 29.7969px;">[![image-1713956541731.png](https://developer.verestro.com/uploads/images/gallery/2024-04/scaled-1680-/image-1713956541731.png)](https://developer.verestro.com/uploads/images/gallery/2024-04/image-1713956541731.png)

</td></tr></tbody></table>

<p class="callout success">**Tip:** In this implementation model your application makes a request to the [`transactionInitialization`](https://developer.verestro.com/books/paytool/page/how-to-integrate#bkmrk-get-transaction-deta) method to create a payment session and then redirect your payer to the Paytool application. From this point on, are fully responsible for all other steps in the process such as execution of the transaction and [threeDs authentication](https://developer.verestro.com/books/paytool/page/use-cases#bkmrk-threeds).</p>

<details id="bkmrk-the-sequence-diagram"><summary>The sequence diagram below illustrates the transaction initialization process step by step</summary>

@startuml  
skinparam ParticipantPadding 30  
skinparam BoxPadding 30  
skinparam noteFontColor #FFFFFF  
skinparam noteBackgroundColor #1C1E3F  
skinparam noteBorderColor #1C1E3F  
skinparam noteBorderThickness 1  
skinparam sequence {  
ArrowColor #1C1E3F  
ArrowFontColor #1C1E3F  
ActorBorderColor #1C1E3F  
ActorBackgroundColor #FFFFFF  
ActorFontStyle bold  
ParticipantBorderColor #1C1E3F  
ParticipantBackgroundColor #1C1E3F  
ParticipantFontColor #FFFFFF  
ParticipantFontStyle bold  
LifeLineBackgroundColor #1C1E3F  
LifeLineBorderColor #1C1E3F  
}  
actor payer  
participant "Customer front" as cfront  
participant "Customer backend" as cback  
participant "Paytool front" as pfront  
participant "Paytool backend" as pback  
payer-&gt;cfront: Pay with Paytool  
cfront-&gt;cback: Payer choosed Paytool  
cback-&gt;pback: Customer authorization + transaction metadata  
pback-&gt;pback: Store transaction metadata + open payment session  
cback&lt;-pback: OK + transaction id + redirect url  
cfront&lt;-cback: OK + transaction id + redirect url  
cfront-&gt;pfront: Redirect + transaction id  
pfront-&gt;pback: Get transaction data + merchant payment methods  
pfront&lt;-pback: OK response  
payer&lt;-pfront: Display transaction + payment methods  
@enduml

</details>### Server to server

An alternative path to carry out a transaction is a [Payment process via API](https://developer.verestro.com/books/paytool/page/overview#bkmrk-payment-process-via-) integration path. Paytool Frontend does not appear in this path. You make all requests directly from your server to the Paytool API methods we described in [technical integration guide](https://developer.verestro.com/books/paytool/page/how-to-integrate).

<details id="bkmrk-the-sequence-diagram-0"><summary>The sequence diagram below illustrates the transaction initialization process step by step</summary>

@startuml  
skinparam ParticipantPadding 30  
skinparam BoxPadding 30  
skinparam noteFontColor #FFFFFF  
skinparam noteBackgroundColor #1C1E3F  
skinparam noteBorderColor #1C1E3F  
skinparam noteBorderThickness 1  
skinparam sequence {  
ArrowColor #1C1E3F  
ArrowFontColor #1C1E3F  
ActorBorderColor #1C1E3F  
ActorBackgroundColor #FFFFFF  
ActorFontStyle bold  
ParticipantBorderColor #1C1E3F  
ParticipantBackgroundColor #1C1E3F  
ParticipantFontColor #FFFFFF  
ParticipantFontStyle bold  
LifeLineBackgroundColor #1C1E3F  
LifeLineBorderColor #1C1E3F  
}  
actor payer  
participant "Customer front" as cfront  
participant "Customer backend" as cback  
participant "Paytool backend" as pback  
payer-&gt;cfront: Pay with Paytool  
cfront-&gt;cback: Payer choosed Paytool  
cback-&gt;pback: Customer authorization + transaction metadata  
pback-&gt;pback: Store transaction metadata + open payment session  
cback&lt;-pback: OK + transaction id  
note right of cfront: At this point, the Customer decides how to present the transaction to the payer  
cback-&gt;pback: Request proper payment method / executing 3D Secure  
cback&lt;-pback: Transaction result  
note right of cfront: At this point, the Customer decides how to present the transaction result to the payer  
@enduml

</details>## Payment methods

Verestro as a PSP provides several different payment methods in Paytool solution. You decide which payment method should be available in Paytool payment form. You decide this during the [onboarding](https://developer.verestro.com/books/merchant-paytool/page/onboarding) process but it is editable whenever necessary. The end user, seeing the available payment methods, can choose the option that is most convenient for him. This chapter describes all payment methods supported by our application.

<table border="1" cellpadding="1" cellspacing="0" id="bkmrk-abbreviation-descrip" style="width: 224px;" width="712"><tbody><tr valign="TOP"><td bgcolor="#002060" style="width: 223px;" width="353"><span style="font-family: Lato; color: #ecf0f1;">**Payment methods in Paytool**</span>

</td></tr><tr valign="TOP"><td style="width: 223px;" width="353">Google Pay™

</td></tr><tr valign="TOP"><td style="width: 223px;" width="353">Apple Pay

</td></tr><tr valign="TOP"><td style="width: 223px;" width="353"><span style="font-family: Lato;">Blik</span>

</td></tr><tr><td style="width: 223px;"><span style="font-family: Lato;">Plain card number</span>

</td></tr></tbody></table>

<p class="callout info"><span lang="en-US">**Note:** Each of the payment methods available from the Paytool frontend is also available with an API to API connection.</span></p>

<p class="callout info"><span lang="en-US">**Note:** It is required that you have created account in the Acquirer's system which will settle your transactions. Verestro Paytool solution has been implemented so that it is possible to process transactions with the participation of various Acquirers. If you require the settlement of the transaction by a new Acquirer – to which we are not yet integrated – there will be required new integration between Verestro and the new Acquirer. You should provide a specification of the Acquirer API.</span></p>

### Plain card number

The most common payment method available in our application is payment using plain card details. This payment method consists in providing a payment form in which the end user can enter his payment card details. The option to pay with plain card details is available at the button shown below:

[![image-1685428055821.png](https://developer.verestro.com/uploads/images/gallery/2023-05/scaled-1680-/image-1685428055821.png)](https://developer.verestro.com/uploads/images/gallery/2023-05/image-1685428055821.png)

After clicking on the payment option using plain card details, the end user is redirected to the specially prepared payment form. Now he is able to provide the appropriate card details and clicks the **Pay** button at the bottom of the screen. At this point, the card details are encrypted and sent to the Paytool backend which requests Acquirer to process transaction. At this moment [threeDs authentication](https://developer.verestro.com/books/paytool/page/use-cases#bkmrk-threeds) process may be required. The payment process using plain card details from the end user's perpective has been shown below:

[![image-1713956617464.png](https://developer.verestro.com/uploads/images/gallery/2024-04/scaled-1680-/image-1713956617464.png)](https://developer.verestro.com/uploads/images/gallery/2024-04/image-1713956617464.png)

<details id="bkmrk-the-sequence-diagram-1"><summary>The sequence diagram below illustrates the transaction with plain card details process step by step</summary>

@startuml  
skinparam ParticipantPadding 30  
skinparam BoxPadding 30  
skinparam noteFontColor #FFFFFF  
skinparam noteBackgroundColor #1C1E3F  
skinparam noteBorderColor #1C1E3F  
skinparam noteBorderThickness 1  
skinparam sequence {  
ArrowColor #1C1E3F  
ArrowFontColor #1C1E3F  
ActorBorderColor #1C1E3F  
ActorBackgroundColor #FFFFFF  
ActorFontStyle bold  
ParticipantBorderColor #1C1E3F  
ParticipantBackgroundColor #1C1E3F  
ParticipantFontColor #FFFFFF  
ParticipantFontStyle bold  
LifeLineBackgroundColor #1C1E3F  
LifeLineBorderColor #1C1E3F  
}  
actor "End User" as user  
participant "Paytool Frontend" as pfront  
participant "Paytool Backend" as pback  
participant "Customer Server" as custback  
participant "Acquirer" as acq  
user-&gt;pfront: User chooses payment by plain card details  
user&lt;-pfront: Redirect end user to the payment form  
user-&gt;pfront: User filling data (CN, CVC, EXP)  
pfront-&gt;pfront: Encrypt data  
pfront-&gt;pback: Perform transaction providing encrypted payment request body  
pback-&gt;pback: Decrypt encrypted payment request body  
pback-&gt;acq: Order transaction  
note left of acq: At this point 3D Secure process may occur  
acq-&gt;pback: Response  
pback-&gt;pfront: Transaction Result  
pback--&gt;pback: Store transaction result  
pfront-&gt;pfront: Redirect end user (success/failure)  
pback-&gt;custback: Send transaction postback to provided URL (optional - configurable)  
note right of pback: Verestro can also send the notification after transaction to the end user(optional)  
custback-&gt;pback: Get transaction status (optional)  
pback-&gt;custback: Return transaction status  
@enduml

</details>#### <span style="font-family: Lato; color: #000000;">Dynamic currency conversion</span>

The DCC functionality is to determine the currency of the payer's card, compare it with the currency used by the merchant selling the goods, and provide the payer with the option of converting currency at our rate or ordering payment leaving the currency conversion to the bank that issued the card. The DCC mechanism is triggered when the currency of the payer's card is different from the sales currency then.

<p class="callout info">**Note:** Currently, DCC functionality is only available for transactions made with Fenige's terminal.  
*Fenige is our partner acquiring institution.*</p>

After entering the card data in the correct field, the currency of the card is determined. If the dynamic currency conversion has been triggered, the following popup will be displayed to the payer and the total amount in the transaction details will be updated:

<table border="1" id="bkmrk--2" style="border-collapse: collapse; width: 100%; border-width: 1px; border-style: hidden;"><colgroup><col style="width: 50%;"></col><col style="width: 50%;"></col></colgroup><tbody><tr><td>[![DCC caluculate 2 cutted.png](https://developer.verestro.com/uploads/images/gallery/2025-02/scaled-1680-/dcc-caluculate-2-cutted.png)](https://developer.verestro.com/uploads/images/gallery/2025-02/dcc-caluculate-2-cutted.png)

</td><td>[![DCC screen.png](https://developer.verestro.com/uploads/images/gallery/2025-02/scaled-1680-/lFRdcc-screen.png)](https://developer.verestro.com/uploads/images/gallery/2025-02/lFRdcc-screen.png)</td></tr></tbody></table>

### Google Pay

Paytool as a registered hosted checkout in the Google Pay™ allows to perform a payment with the card from the Google Pay™ Wallet. Using our application your payer can choose the Google Pay™ as the payment method from the Verestro Paytool payment methods list. The option to pay with Google Pay™ card token is available at the button shown below:

[![image-1685428002241.png](https://developer.verestro.com/uploads/images/gallery/2023-05/scaled-1680-/image-1685428002241.png)](https://developer.verestro.com/uploads/images/gallery/2023-05/image-1685428002241.png)

After clicking on the Google Pay™ payment option, the Google Pay™ Wallet popup is displayed. The payer should select the appropriate card from the Google Pay™ Wallet which is then encrypted on the Google Pay™ side and transferred to our application. We will decrypt obtained data and transfer them to the Acquirer in the transaction request. At this moment [threeDs authentication](https://developer.verestro.com/books/paytool/page/use-cases#bkmrk-threeds) process may be required but it will be handled on our side. The payment process using Google Pay™ card payment token from the end user's perpective has been shown below:

[![image-1689246683126.png](https://developer.verestro.com/uploads/images/gallery/2023-07/scaled-1680-/image-1689246683126.png)](https://developer.verestro.com/uploads/images/gallery/2023-07/image-1689246683126.png)

<details id="bkmrk-the-sequence-diagram-2"><summary>The sequence diagram below illustrates the payment process using Google Pay™ card payment token step by step</summary>

@startuml  
skinparam ParticipantPadding 30  
skinparam BoxPadding 30  
skinparam noteFontColor #FFFFFF  
skinparam noteBackgroundColor #1C1E3F  
skinparam noteBorderColor #1C1E3F  
skinparam noteBorderThickness 1  
skinparam sequence {  
ArrowColor #1C1E3F  
ArrowFontColor #1C1E3F  
ActorBorderColor #1C1E3F  
ActorBackgroundColor #FFFFFF  
ActorFontStyle bold  
ParticipantBorderColor #1C1E3F  
ParticipantBackgroundColor #1C1E3F  
ParticipantFontColor #FFFFFF  
ParticipantFontStyle bold  
LifeLineBackgroundColor #1C1E3F  
LifeLineBorderColor #1C1E3F  
}  
actor "End User" as user  
participant "Paytool Frontend" as pfront  
participant "Paytool Backend" as pback  
participant "Google Pay" as gpay  
participant "Customer Server" as custback  
participant "Acquirer" as acq  
user-&gt;pfront: End user chooses payment by Google Pay  
pfront-&gt;gpay: Open end user Google Wallet  
user&lt;--gpay: Opens end user's Google Wallet  
user--&gt;gpay: Choose card from Google Wallet  
gpay-&gt;gpay: Encrypt chosen card token data  
pfront&lt;-gpay: Provide encrypted card token data  
pfront-&gt;pback: Order transaction  
pfront--&gt;pback: Provide encrypted card token data  
pback-&gt;pback: Decrypt encrypted card token data  
pback-&gt;acq: Order transaction  
note left of acq: At this point 3D Secure process may occur  
acq-&gt;pback: Response  
pback-&gt;pfront: Transaction Result  
pback--&gt;pback: Store transaction result  
pfront-&gt;pfront: Redirect end user (success/failure)  
pback-&gt;custback: Send transaction postback to provided URL (optional - configurable)  
note right of pback: Verestro can also send the notification after transaction to the end user (optional)  
custback-&gt;pback: Get transaction status (optional)  
pback-&gt;custback: Return transaction status  
@enduml

</details>#### Google Pay payment via API

Alternatively Verestro as a registered PSP in the Google Pay™ allows to perform a payment with card token generated by Google. This payment option provides a backend to backend oriented solution. In this payment model you must be [registered merchant in Google Pay™](https://developer.verestro.com/books/paytool/page/onboarding#bkmrk-register-and-integra) to be able to get a card payment token from Google Pay™.

To use this option your API should be integrated with the `<a href="https://developer.verestro.com/books/paytool/page/how-to-integrate#bkmrk-google-pay-transacti">googlePayTransaction</a>` method provided by Paytool API. By using this solution you need to display Google Pay™ Wallet in your application by your own. After selecting the Google Pay™ as the payment option a payer chooses proper card from Google Pay™ Wallet. After that action you get encrypted card payment token from Google Pay™. Card payment token is encrypted on the Google Pay™ side with Verestro's public key. You have to provide this encrypted token to Paytool API by using `<a href="https://developer.verestro.com/books/paytool/page/how-to-integrate#bkmrk-google-pay-transacti">googlePayTransaction</a>` method. If you do this, we will handle transaction process on our side. At this moment 3D Secure process may be required and you need to handle it on your side using [threeDs authentication](https://developer.verestro.com/books/paytool/page/use-cases#bkmrk-threeds) methods provided by Paytool API.

<details id="bkmrk-the-sequence-diagram-3"><summary>The sequence diagram below illustrates the payment process using Google Pay™ card payment token API to API step by step</summary>

@startuml  
skinparam ParticipantPadding 30  
skinparam BoxPadding 30  
skinparam noteFontColor #FFFFFF  
skinparam noteBackgroundColor #1C1E3F  
skinparam noteBorderColor #1C1E3F  
skinparam noteBorderThickness 1  
skinparam sequence {  
ArrowColor #1C1E3F  
ArrowFontColor #1C1E3F  
ActorBorderColor #1C1E3F  
ActorBackgroundColor #FFFFFF  
ActorFontStyle bold  
ParticipantBorderColor #1C1E3F  
ParticipantBackgroundColor #1C1E3F  
ParticipantFontColor #FFFFFF  
ParticipantFontStyle bold  
LifeLineBackgroundColor #1C1E3F  
LifeLineBorderColor #1C1E3F  
}  
participant "End user" as user  
participant "Customer Application" as app  
participant "Google Pay" as gp  
participant "Paytool Backend" as tps  
participant "Acquirer" as acq  
note right of user: User wants to pay with Google Pay  
user-&gt;app: Pay with Google Pay and choose card  
app-&gt;gp: Requests for card token  
gp-&gt;gp: Encrypts card token with Verestro pub key  
app&lt;-gp: Returns encrypted card token  
app-&gt;tps: Requests token payment  
tps-&gt;tps: Decrypts card token  
tps-&gt;acq: Orders transaction  
tps&lt;-acq: Transaction status  
note left of acq: At this point 3D Secure process may occur  
app&lt;-tps: Transaction status  
user&lt;-app: Transaction status  
user&lt;--tps: Sends email notification - optional  
@enduml

</details><p class="callout warning">**Important:** If you use Paytool with [Payment process via API](https://developer.verestro.com/books/paytool/page/overview#bkmrk-payment-process-via-) integration path, make sure you are a registered merchant in the Google Pay™ system. This does not apply to Customers using the [Redirect your payer](https://developer.verestro.com/books/paytool/page/overview#bkmrk-redirect-your-payer) route.</p>

<p class="callout info">**Note:** Google Pay™ provides a <span style="text-decoration: underline;">[Google Pay Web integration checklist](https://developers.google.com/pay/api/web/guides/test-and-deploy/integration-checklist)</span> that will help you with the integration step by step. The documentation is available after whitelisting in Google Pay™ system. The whitelisting process is performed by Google Pay™ during the Customer's merchant account registration process.</p>

<p class="callout info">**Note:** Google Pay™ provides <span style="text-decoration: underline;">[Google Pay Web Brand Guidelines](https://developers.google.com/pay/api/web/guides/brand-guidelines)</span> that presents branding requirements for web merchants registered in Google Pay™. You must meet these requirements so that you can allow his payers to pay via the Google Pay™ solution.</p>

### Apple Pay

Verestro as a PSP registered in the Apple Pay™ allows to perform a payment with card token generated by Apple. Using our application your payer can choose the Apple Pay™ as the payment method from the Paytool payment methods list. The option to pay with Apple Pay™ card token is available at the button shown below:

[![image-1699524383207.png](https://developer.verestro.com/uploads/images/gallery/2023-11/scaled-1680-/image-1699524383207.png)](https://developer.verestro.com/uploads/images/gallery/2023-11/image-1699524383207.png)

<p class="callout danger">**Warning!** Apple Pay payment method is available in Safari web browser only.</p>

After clicking on the Apple Pay™ payment option, the Apple Pay™ Wallet popup is displayed. End user should select the appropriate card from the Apple Pay™ Wallet popup which is then encrypted on the Apple Pay™ side and transferred to our application. We decrypt obtained data and transfer them to the Acquirer in the transaction request. At this moment [threeDs authentication](https://developer.verestro.com/books/paytool/page/use-cases#bkmrk-threeds) process may be required. The payment process using Apple Pay™ card payment token from the end user's perpective has been shown below:

[![image-1699526152020.18.03.png](https://developer.verestro.com/uploads/images/gallery/2023-11/scaled-1680-/image-1699526152020-18-03.png)](https://developer.verestro.com/uploads/images/gallery/2023-11/image-1699526152020-18-03.png)

<details id="bkmrk-the-sequence-diagram-4"><summary>The sequence diagram below illustrates the payment process using Apple Pay™ card payment token step by step</summary>

@startuml  
skinparam ParticipantPadding 30  
skinparam BoxPadding 30  
skinparam noteFontColor #FFFFFF  
skinparam noteBackgroundColor #1C1E3F  
skinparam noteBorderColor #1C1E3F  
skinparam noteBorderThickness 1  
skinparam sequence {  
ArrowColor #1C1E3F  
ArrowFontColor #1C1E3F  
ActorBorderColor #1C1E3F  
ActorBackgroundColor #FFFFFF  
ActorFontStyle bold  
ParticipantBorderColor #1C1E3F  
ParticipantBackgroundColor #1C1E3F  
ParticipantFontColor #FFFFFF  
ParticipantFontStyle bold  
LifeLineBackgroundColor #1C1E3F  
LifeLineBorderColor #1C1E3F  
}  
actor "End User" as user  
participant "Paytool Frontend" as pfront  
participant "Paytool Backend" as pback  
participant "Apple Pay" as gpay  
participant "Customer Server" as custback  
participant "Acquirer" as acq  
user-&gt;pfront: End user chooses payment by Apple Pay  
pfront-&gt;gpay: Open end user's Apple Pay Wallet  
user&lt;--gpay: Opens end user's Apple Pay Wallet  
user--&gt;gpay: Choose card from Apple Pay Wallet  
note left of user: At this point Apple Pay may require user authorization  
gpay-&gt;gpay: Encrypt chosen card token data  
pfront&lt;-gpay: Provide encrypted card token data  
pfront-&gt;pback: Order transaction  
pfront--&gt;pback: Provide encrypted card token data  
pback-&gt;pback: Decrypt encrypted card token data  
pback-&gt;acq: Order transaction  
note left of acq: At this point 3D Secure process may occur  
acq-&gt;pback: Response  
pback-&gt;pfront: Transaction Result  
pback--&gt;pback: Store transaction result  
pfront-&gt;pfront: Redirect end user (success/failure)  
pback-&gt;custback: Send transaction postback to provided URL (optional - configurable)  
note right of pback: Verestro can also send the notification after transaction to the end user (optional)  
custback-&gt;pback: Get transaction status (optional)  
pback-&gt;custback: Return transaction status  
@enduml

</details><p class="callout info">**Note:** At this moment Apple Pay biometric authorization may be required.</p>

<p class="callout info">**Note:** Payment using the Apple Pay Wallet is only possible if the payer uses MacOS.</p>

### Blik

Our solution supports cardless payments using the Blik code. The end user can choose the Blik as the payment method from the Verestro Paytool payment methods list. The option to pay with Blik code is available at the button shown below:

[![image-1685523665104.png](https://developer.verestro.com/uploads/images/gallery/2023-05/scaled-1680-/image-1685523665104.png)](https://developer.verestro.com/uploads/images/gallery/2023-05/image-1685523665104.png)After selecting this payment method, the end user must provide his e-mail address in the proper field in displayed popup and then confirm the willingness to make the transaction. Blik as an external service, in response opens a view that allows end user to enter the 6 digits code. This step of the process takes place outside the Verestro. The 6 digits Blik code is generated in the end user's bank application. The payment process using Blik code from the end user's perpective has been shown below:

<table border="0" id="bkmrk--8" style="border-collapse: collapse; width: 100%; height: 29.7969px; border-style: hidden;"><tbody><tr style="height: 29.7969px;"><td style="width: 50%; height: 29.7969px;">[![image-1687851945379.png](https://developer.verestro.com/uploads/images/gallery/2023-06/scaled-1680-/image-1687851945379.png)](https://developer.verestro.com/uploads/images/gallery/2023-06/image-1687851945379.png)

</td><td style="width: 50%; height: 29.7969px;">[![image-1687852047098.png](https://developer.verestro.com/uploads/images/gallery/2023-06/scaled-1680-/image-1687852047098.png)](https://developer.verestro.com/uploads/images/gallery/2023-06/image-1687852047098.png)

</td></tr></tbody></table>

<details id="bkmrk-the-sequence-diagram-5"><summary>The sequence diagram below illustrates the payment process using Blik step by step</summary>

@startuml  
skinparam ParticipantPadding 30  
skinparam BoxPadding 30  
skinparam noteFontColor #FFFFFF  
skinparam noteBackgroundColor #1C1E3F  
skinparam noteBorderColor #1C1E3F  
skinparam noteBorderThickness 1  
skinparam sequence {  
ArrowColor #1C1E3F  
ArrowFontColor #1C1E3F  
ActorBorderColor #1C1E3F  
ActorBackgroundColor #FFFFFF  
ActorFontStyle bold  
ParticipantBorderColor #1C1E3F  
ParticipantBackgroundColor #1C1E3F  
ParticipantFontColor #FFFFFF  
ParticipantFontStyle bold  
LifeLineBackgroundColor #1C1E3F  
LifeLineBorderColor #1C1E3F  
}  
actor "End User" as user  
participant "Paytool Frontend" as pfront  
participant "Paytool Backend" as pback  
participant "Acquirer" as acq  
participant "Blik" as blik  
participant "Customer Server" as custback  
user-&gt;pfront: End user chooses payment by Blik (1)  
pfront-&gt;pback: Requests for payment by Blik (2)  
pback-&gt;acq: Orders Blik transaction (3)  
acq-&gt;blik: Internal request to Blik system (4)  
acq&lt;-blik: Response from Blik system with HTML payment Base64 encoded form (5)  
pback&lt;-acq: Provides Blik's response (5.1)  
pfront&lt;-pback: Provides Blik's response (5.2)  
pfront-&gt;pfront: Decode Blik HTML form (6)  
user&lt;-pfront: Displays Blik HTML form (7)  
user-&gt;user: Enters Blik's 6 digits code (8)  
user--&gt;blik: After form submitting request to Blik system is triggered (9)  
pfront&lt;--blik: Redirects to Paytool Frontend (10)  
user&lt;--pfront: Shows progress bar because the user has to wait for transaction status (11)  
acq&lt;--blik: Webhook with information about Blik's transaction status (12)  
pback&lt;--acq: Webhook with information about Blik's transaction status (12.1)  
pfront-&gt;pback: Get status of the Blik transaction (13)  
pfront&lt;-pback: Provides Blik transaction status (14)  
user&lt;-pfront: Displays transaction status (15)  
custback&lt;--pback: Send transaction postback to provided URL (16) (optional - configurable)  
@enduml

</details>## ThreeDs authentication

Transactions using payment cards usually require additional authentication of the end user (card holder). In accordance with the Europenian Union directive PSD2, the Paytool solution uses the threeDs protocol version 2.0 for the authentication process. The threeDs process consists in asking the card issuer whether additional authentication of the card holder is necessary or not. It depends on the bank's response whether the threeDs process will be necessary to perform. This is determined by one of two statuses that the bank returns during the transaction process: [`FRICTIONLESS`](https://developer.verestro.com/books/paytool/page/use-cases#bkmrk-%40startumlskinparam-p-2) or [`CHALLENGE`](https://developer.verestro.com/books/paytool/page/use-cases#bkmrk-challenge). The meaning of each status is described in the section [ThreeDs modes](https://developer.verestro.com/books/paytool/page/use-cases#bkmrk-threeds-modes). We take responsibility for performing the threeDs authentication process. The sequence diagrams below illustrates the threeDs authentication process step by step separatly for both cases: [`FRICTIONLESS`](https://developer.verestro.com/books/paytool/page/use-cases#bkmrk-%40startumlskinparam-p-2) or [`CHALLENGE`](https://developer.verestro.com/books/paytool/page/use-cases#bkmrk-challenge).

### ThreeDs modes

<table class="tableblock frame-all grid-all spread" id="bkmrk-environemt-base-url-" style="width: 87.284%;"><colgroup><col style="width: 23.8331%;"></col><col style="width: 76.1669%;"></col></colgroup><tbody><tr><td bgcolor="#002060" style="height: 22.3906px;" width="353"><span style="font-family: Lato; color: #ecf0f1;">ThreeDs mode</span>

</td><td bgcolor="#002060" style="height: 22.3906px;" width="353"><span style="color: #ffffff;">Description</span>

</td></tr><tr><td class="tableblock halign-left valign-top">`<span style="font-family: -apple-system, BlinkMacSystemFont, Segoe UI, Oxygen, Ubuntu, Roboto, Cantarell, Fira Sans, Droid Sans, Helvetica Neue, sans-serif;">FRICTIONLESS</span>`

</td><td class="tableblock halign-left valign-top">The response containing the `FRICTIONLESS` mode denotes that payment is successfully finnished. Additional 3DS authentication is not required.

</td></tr><tr><td class="tableblock halign-left valign-top">`<span style="font-family: -apple-system, BlinkMacSystemFont, Segoe UI, Oxygen, Ubuntu, Roboto, Cantarell, Fira Sans, Droid Sans, Helvetica Neue, sans-serif;">CHALLENGE</span>`

</td><td class="tableblock halign-left valign-top">The response containing this mode denotes that the card holder must be additionally authenticated. Along with the `CHALLENGE` mode, the Bank also returns an encoded HTML template, which is displayed to the end user in the Verestro Paytool Frontend, thus allowing the end user to perform 3DS authentication.

</td></tr></tbody></table>

#### `FRICTIONLESS`

In this threeDs mode there is not any additional action from the end user side required.

<details id="bkmrk-the-sequence-diagram-6"><summary>The sequence diagram below illustrates the threeDs process for frictionless mode step by step</summary>

@startuml  
skinparam ParticipantPadding 30  
skinparam BoxPadding 30  
skinparam noteFontColor #FFFFFF  
skinparam noteBackgroundColor #1C1E3F  
skinparam noteBorderColor #1C1E3F  
skinparam noteBorderThickness 1  
skinparam sequence {  
ArrowColor #1C1E3F  
ArrowFontColor #1C1E3F  
ActorBorderColor #1C1E3F  
ActorBackgroundColor #FFFFFF  
ActorFontStyle bold  
ParticipantBorderColor #1C1E3F  
ParticipantBackgroundColor #1C1E3F  
ParticipantFontColor #FFFFFF  
ParticipantFontStyle bold  
LifeLineBackgroundColor #1C1E3F  
LifeLineBorderColor #1C1E3F  
}  
actor "End User" as user  
participant "Paytool Frontend" as pfront  
participant "Paytool Backend" as pback  
participant "Acquirer" as acq  
participant "Bank" as bank  
user-&gt;pfront: End user confirmed transaction (1)  
note right of user: For example the end user choosed payment with plain card number (1.1)  
pfront-&gt;pback: Provide transaction request to perform (2)  
pback-&gt;acq: Provide transaction request to perform (3)  
acq-&gt;bank: contact with end user's bank (4)  
bank-&gt;acq: Return FRICTIONLESS status - transaction succeed (5)  
acq-&gt;pback: Provide bank's response (6)  
pback-&gt;pfront: Provide bank's response (6.1)  
pfront-&gt;user: Display transaction status (7)  
@enduml

</details>#### `CHALLENGE`

In this threeDs mode the end user authentication is required. Authentication takes place on the threeDs bank template displayed by the Verestro Paytool application to the end user during the transaction process.

<details id="bkmrk-the-sequence-diagram-7"><summary>The sequence diagram below illustrates the threeDs process for challenge mode step by step</summary>

@startuml  
skinparam ParticipantPadding 30  
skinparam BoxPadding 30  
skinparam noteFontColor #FFFFFF  
skinparam noteBackgroundColor #1C1E3F  
skinparam noteBorderColor #1C1E3F  
skinparam noteBorderThickness 1  
skinparam sequence {  
ArrowColor #1C1E3F  
ArrowFontColor #1C1E3F  
ActorBorderColor #1C1E3F  
ActorBackgroundColor #FFFFFF  
ActorFontStyle bold  
ParticipantBorderColor #1C1E3F  
ParticipantBackgroundColor #1C1E3F  
ParticipantFontColor #FFFFFF  
ParticipantFontStyle bold  
LifeLineBackgroundColor #1C1E3F  
LifeLineBorderColor #1C1E3F  
}  
actor "End User" as user  
participant "Paytool Frontend" as pfront  
participant "Paytool Backend" as pback  
participant "Acquirer" as acq  
participant "Bank" as bank  
user-&gt;pfront: End user confirmed transaction (1)  
note right of user: For example the end user choosed payment with plain card number (1.1)  
pfront-&gt;pback: Provide transaction request to perform (2)  
pback-&gt;acq: Provide transaction request to perform (3)  
acq-&gt;bank: contact with end user's bank (4)  
bank-&gt;acq: Return CHALLENGE status along with bank HTML template (5)  
acq-&gt;pback: Provide bank's response (6)  
pback-&gt;pfront: Provide bank's response (6.1)  
pfront-&gt;pfront: Decode bank HTML template (7)  
pfront-&gt;user: Display bank content to the end user (8)  
user--&gt;bank: Perform 3DS authentication (9)  
user&lt;--bank: Authentication succeed (10)  
acq&lt;-bank: Provide success status and authentication ID (11)  
pback&lt;-acq: Provide success status and authentication ID (11.1)  
pfront&lt;-pback: Provide success status and authentication ID (11.2)  
pfront-&gt;pback: Finalize transaction and provide authentication ID (12)  
pback-&gt;acq: Finalize transaction and provide authentication ID (12.1)  
acq-&gt;bank: Finalize transaction (12.2)  
bank-&gt;acq: Transaction succeed (13)  
acq-&gt;pback: Provide transaction status (14)  
pback-&gt;pfront: Provide transaction status (15)  
pfront-&gt;user: Display transaction status (16)  
@enduml

</details>## Transaction result

Depending on whether the transaction was successful or not, the end user will see the appropriate status on the screen. From the status screen, he is able to return to the store's website manually - by clicking the **Return to the shop** button or wait for an automatic redirection. At the same time, we will send you post-transaction notification containing the status and details of the transaction. Depending on the configuration of your merchant account, an e-mail notification may be sent to the end user. Transaction status views from the end user's perspective are presented below:

<table border="0" id="bkmrk-%C2%A0-0" style="border-collapse: collapse; width: 100%; border-style: hidden;"><tbody><tr><td style="width: 50%; border-style: dotted;">[![image-1684330553924.png](https://developer.verestro.com/uploads/images/gallery/2023-05/scaled-1680-/image-1684330553924.png)](https://developer.verestro.com/uploads/images/gallery/2023-05/image-1684330553924.png)</td><td style="width: 50%; border-style: dotted;">[![image-1684330621724.png](https://developer.verestro.com/uploads/images/gallery/2023-05/scaled-1680-/image-1684330621724.png)](https://developer.verestro.com/uploads/images/gallery/2023-05/image-1684330621724.png)</td></tr></tbody></table>

### Notification after transaction

As mentioned in the [Transaction result](https://developer.verestro.com/books/paytool/page/use-cases#bkmrk-notifications) chapter, Paytool solution supports the sending of post-transaction notifications informing you about the status of a given transaction made in your context. This functionality is optional and it is up to you to decide whether you want to receive post-transaction notifications. This decision is made during the [onboarding](https://developer.verestro.com/books/merchant-paytool/page/onboarding) process and always can be edited. We recommend using this functionality, as this allow you to receive information on each of the transactions made using Verestro Paytool.

<p class="callout warning">**Important:** In order for you to receive [notification after transaction](https://developer.verestro.com/books/paytool/page/how-to-integrate#bkmrk-transaction-postback), you must define your own endpoint. You can provide us your notification URL address during the [onboarding](https://developer.verestro.com/books/merchant-paytool/page/onboarding) process or later. We will use this notification URL address to send you post-transaction notifications. </p>

<details id="bkmrk-example-request-body"><summary>Post-transaction notification example sent by Verestro Paytool to the Customer</summary>

```json
{
  "transactionId": "string",
  "orderNumber": "9afds032dad",
  "transactionState": "FAILED",
  "amount": 0,
  "message": "string",
  "currency": "string",
  "externalTransactionId": "string",
  "transactionType": "ONE_TIME_PAYMENT",
  "cardDetails": {
    "cardProvider": "MASTERCARD",
    "cardNumber": "512485******4875"
  },
  "failedDetails": {
    "code": "SYSTEM_ERROR",
    "message": "E0200: Transaction rejected, card is blocked"
  }
}
```

</details>### End user notifications

As mentioned in the [Transaction result](https://developer.verestro.com/books/paytool/page/use-cases#bkmrk-notifications) chapter, Paytool solution supports an e-mail notification sending. Such notification contains the status and details of the transaction. This message is purely informative so that the payer knows that a transaction has been made in the context of his chosen payment instrument. This functionality is optional and it is up to you to decide whether you us to send end users notifications after the transaction. This decision is made during the [onboarding](https://developer.verestro.com/books/merchant-paytool/page/onboarding) process and always can be edited.

<p class="callout info">**Note:** The appearance of the e-mail notification is configurable.</p>

<table class="tableblock frame-all grid-all spread" id="bkmrk-example-e-mail-notif" style="width: 99.1358%;"><colgroup><col style="width: 50.064%;"></col><col style="width: 50.064%;"></col></colgroup><tbody><tr><td bgcolor="#002060" style="height: 22.3906px; width: 176.5px;" width="353"><span style="color: #ffffff;">Example e-mail notification after successful transaction</span>

</td><td bgcolor="#002060" style="height: 22.3906px; width: 176.5px;" width="353"><span style="color: #ffffff;">Example e-mail notification after failed transaction</span>

</td></tr><tr><td class="tableblock halign-left valign-top">[![image-1689254790584.png](https://developer.verestro.com/uploads/images/gallery/2023-07/scaled-1680-/image-1689254790584.png)](https://developer.verestro.com/uploads/images/gallery/2023-07/image-1689254790584.png)

</td><td>[![image-1689254800782.png](https://developer.verestro.com/uploads/images/gallery/2023-07/scaled-1680-/image-1689254800782.png)](https://developer.verestro.com/uploads/images/gallery/2023-07/image-1689254800782.png)

</td></tr></tbody></table>