Hi,
When you use a single file, you need to have full distributions for each transaction. You are creating an AP transaction, and assigning a payment to it. This does not create a cash-basis transaction that overrides the AP process. If you want to do that, you need to use the Bank Transaction entry integration. This will credit cash and debit whatever your specified account is.
I will assume you want to create a payable and a payment together though. Your single source integration file should have a sequence key by which to group transactions. Each AP transaction will have a minimum of two lines, one for the PAY distribution and one for the PURCH distribution. The PAY one is required. The debits and credits are also included. You can use a single amount though, and tell IM that negative numbers are credits. You will need to supply the credit to AP.
I assume you are comfortable with this. For the credit card payment, if you do not have the credit card set up in GP, use the cash option in the mapping setup for the AP transaction.
The credit card information should be setup and grouped together with the header items so the single file only tries to import them once. This would be "Card Name, Receipt Number, Date, and Payment Number. Make sure to set your options to Use Field Rules.
To reiterate, on the setup for the single file, you still need two sources that use the same file. For the header, only select the header and credit card items. Group together all the header items to get one line item per AP transaction. Obviously, all columns for each transaction must match, otherwise you will end up with more than one group per header record.
For the details, uncheck all the header and CC items to show the distributions.
Create a relationship using your sequence key column, and test your integration. This will create both an AP transaction and a payment. You also need to make sure that you have the ability in GP to create payments on the fly, otherwise this integration will fail.