Selected bank details for customer &1 are not valid

What causes this issue?

The bank details were copied from the template document. Checking of
bank details from the template was activated.
You want to use bank details for a customer for payment, but these bank
details are not in the customer master record or are no longer valid.

System Response

The request cannot be saved.

How to fix this error?

If the bank details do not currently exist in the master record but are
to be retained, you can confirm this by accessing the payer data (Ctrl +
F10) or by deriving valid bank details by entering the customer again.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.