How to create a Credit Card credit through Vendor Invoices:

Create 0 invoice through Vendor Invoices using your credit amount

Then open the bank register for the credit card.  Enter the credit through the bank register.  After you save from the credit card entry screen, the distribution screen comes up, enter the credit account using the same account that was used in the invoice entry in Vendor Invoices.    

If your credit invoice is to a project this will make the project correct.   This will also get your financial statement correct.  Your vendor Invoice list will not show the credit invoice only a zero invoice.