Rick - I handle a very large volume of payments through AmEx each month. I have set American Express up as a vendor and enter all invoices into the vendor, using the correct g/l code for each invoice. I also pay for sister properties using the intercompany process. I then make an online payment and in M3, I post it to A/R Other. After all of the invoices are entered and I know they are balanced to the statement. I enter a credit invoice in the total amount using the A/R Other account as the g/l so that account is zeroed out each month. I also set American Express up as an ACH payment only so I don't have to remember to pay it as an ACH.
Hope this is helpful -
Vacation Myrtle Beach/Legacy Business Solutions