1. Create a liability account in your chart of accounts and call it Credit Card Transfer, or something similar.
2. Create a payable to Credit Card B in the Payables Journal for the balance of Credit Card A, using the Credit Card Transfer liability account as the Ledger Account.
3. In Vendor Payments, choose the Credit Card Transfer account as the Disc/Adj Acct.
The Cash Account that is selected is not important, as the transaction will not affect it.
4. Highlight the payable for Credit Card A, and enter zero for the Amt Paid.
5. TAB to the Disc/Adj field, type in the amount of the payable, then click TAB or RETURN.
If you have more than one payable for Credit Card A, you should repeat Step 4 for each payable.
You may want to change the document number to TR(date) to help identify the transfer.
6. Click Save.
This records a credit to the Credit Card Transer account, which washes out the debit that was recorded in the Payables Journal in Step 2. You should now have just the balance in Credit Card B in your Accounts Payable report and in Vendor Payments.