when i pay amex from my personal account it credits the payment to my business account. any idea why?
Where a transaction, presumably originating in your personal checking account, goes is determined by what account name (enclosed in Square brackets [account name]) you use in that checking transaction.
But, I'm not entirely clear as to what you're doing. Are you inputting the payment into the Amex register (as a transfer) or into a checking register (again, as a transfer)?