Payment Reason in Payment File Submitted to Bank

Summary:

One of our suppliers require that we submit the plan number (ex. company benefits plan number) in our payment file which is submitted to the bank.

Content (please ensure you mask any confidential information):

We have an issue where we need to submit the plan number in our payment file to the bank (ACH Payment) in order to let the supplier know what plan the payment is for. If we do not send the number it delays payment and causes other issues. I added a payment reason code which could be added to the invoice, but doing that did not correct the issue, In looking at the file, the field on the payment file where the code needs to be populated is 26 Reason 1. Would anyone know what field on the invoice/payment where