The Dynamics Support team explains Custom fields you can or can’t do for PM EFT formats in Microsoft Dynamics GP . You’re going to want to bookmark this link.
Custom fields you can or can’t do for PM EFT formats in Microsoft Dynamics GP – Microsoft Dynamics GP Community
Payables & ReceivablesMicrosoft & the GP Ecosystem
Archived post from 2014. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.