Diagnosis
Either no bank details have been entered in the customer/vendor master record or the bank details cannot be used for the payment method entered.
For instance, a payment method can require
that there is a direct debit authorization,
that the business partner bank must be domestic,
that the bank details IBAN or SWIFT code must be known,
or that a mandate has been granted. You should note in this case that the mandate must be active so that it can be used in the payment process. You should also check whether a mandate has been specified in the line item.
System Response
The payment method entered is not accepted.
Procedure
If the customer/vendor master record is maintained incompletely, complete the bank details. Proceed Otherwise, you have to use a payment method that does not require bank details (for example, a check) or that can use the bank details entered for the business partner.
SOLUTION:
STEP 1: Go to Transaction code BP (Business Partner) > Select your Customer/vendor
STEP 2: Click on Edit mode > Go to Payment Transaction Tab > Provide Bank details of Customer/Vendor and SAVE
Thanks,
Adharsh K S