Allocating a Credit from Two Separate Invoices
To allocate a credit from two separate invoices (see first screenshot below) to one, you must first select the credit invoice and then select the MOVE TO CREDIT button.
You can then go to the CREDIT tab and allocate the payments as normal.
Please note, when allocating a credit manually, you will need to create an A/R Manual Credit code. Once this code is created, you will be able allocate a credit as detailed above.