Clients/Customers can tell their bank to allow direct debits up to a certain amount. When a direct debit is suggested with an amount larger the maximum amount the bank will block the direct debit. This can result in cost for a rejected direct debit which can be avoided by adding the maximum amount in F&O.
My suggestion is twofold:
1. Add a maximum amount on the direct debit mandate on the customer
The second part could through two options:
2.1 Add an option with options block / split; The block option with stop the user from creating the payment transaction when going further in the payment proposal. Split option will make one transaction of the maximum amount and create a next transaction for the remaining amount (unless this is also above the maximum amount, than a third transaction will be created, etc.)
2.2 Add the new maximum amount field to the payment journal line form so the user can do a manual verification of the amount vs the payment transaction.