How can I secure the change of the payment channel during the transaction?
To protect against channel changes, implement the selection of channels on the store side and create transactions via API using the create method.
After redirection to the transaction panel, the user will no longer have the option to change the payment method to a different one than that available within the selected group (eg PBL and e-transfer of the same bank).
The easiest way to do this integration is to use the dedicated PHP Tpay libraries, where the BankSelectionAPI.php file is responsible for displaying the selection of banks on the page, and the TransactionApiExample.php file is responsible for receiving the selected payment group and sending the remaining transaction parameters.
In the aforementioned files should be supplemented with the access data of the seller and the transfer of the remaining order data (in the createTransaction method).
If you do not use the PHP programming language, you must make the selection of banks available according to the group documentation.