Suggestion:
This definition of bank code in bank service station master can be made optional based on the service station required flag in bank master. If the service station required flag is ‘No’ then the system will allow the user to confirm the transaction without the service station definition.
For Bank Master goto Finance-> Finance settings-> Masters-> Bank Related->Bank Master
If in Bank Master service station required flag is ‘Yes’. Then map the bank with station code in Bank Service Master.
For Bank Service Master goto Finance-> Finance settings-> Masters-> Bank Related->Bank Service Master.