Handling suppliers paid with multiple payment methods

Summary:

We have a supplier to whom we pay a monthly fixed fee via direct debit, and we use EFT for other miscellaneous services. Recently, an invoice for the fixed fee was mistakenly processed as an EFT payment, resulting in a duplicate payment. We are exploring ways to prevent this from happening again.

One idea we had was to create two supplier sites with different payment methods, but there's still a risk that the AP accountant might select the wrong site. We also looked into configuring the payment method at the Purchase Order level, but couldn't find a solution.

Has anyone encountered a similar issue and found an effective way to prevent such errors? Any insights or suggestions would be greatly appreciated.