I understand that handling payments to maintain accurate books can be challenging. I'm here to guide you address the issue that you have, @rod. 

To avoid double entry, you'll need to delete the credit that was created and edit the deposit. When editing the deposit, you can select the Accounts Receivable account to properly apply the existing credit to the customer's invoice. This help ensure that there is no duplication of entries.

I have an article here that you can use as a reference in the future: Create and apply credit memos in QuickBooks for Mac.

Furthermore, I've added this resource that contains details to help you efficiently manage your QBDT for Mac: QuickBooks Desktop Mac Guide.

Let us know how it goes or if you still have other questions about credit memos. I'll be in touch. Keep safe.