How to Customize NACHA (ACH) Formats in SAP: Possible Edge Cases and How to Fix Them

ACH is how most US companies move money between bank accounts, and NACHA defines the file format that every ACH payment has to follow. SAP delivers standard NACHA formats, but banks and clients almost always ask for something the standard does not produce, which is where customization comes in. In this post, I will walk you through the SAP implementation of the standard NACHA (ACH) format, highlight possible future problems, and show how to customize ACH whether it is a function-module-based or DME-engine-based format. The ACH Format (NACHA) In OBPM1 we can see all formats, both SAP standard ones and custom ones. Formats can be function-module-based or DME-engine-based. If there is no checkbox marked “Mapping using DME engine,” then it is an FM-based format; in other words, a hardcoded format. ACH is an example of such a format. If it is marked, then the format is created via the DME engine (transactions DMEE/DMEEX), which we can call configuration-based. FM-based formats usually have a sequence of FMs that corresponds to the file structure. For example, the ACH format looks like this: These FMs essentially hardcode the file structure: the file header (record starts with 1; highlig...