When the customer opens the Payment Link, he's redirected on Bridge :

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Is your app a sandbox app?

If your app is a sandbox app, then you will see a full list of banks, but only the ones with a sandbox environment will work and redirect you to their interface. To see the list of banks which are compatible with a sandbox app, please see this list

After the customer is redirected to his bank interface, he logs in with his credentials and validate the payment with a Strong Customer Authentication. The bank also displays the details of the payment.