Frank Hamelly provide a solution to a scenario where credit card fees need to be billed back to a customer. See how he did it Using the Miscellaneous field on SOP transactions to recapture Credit Card fees.
Using the Miscellaneous field on SOP transactions to recapture Credit Card fees in Dynamics GP
Archived post from 2010. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.