Customer Payment Received Twice for One Invoice

Hello All,

I have a situation where a customer payment was received twice for the same invoice.  The second "fake" payment is now an open item in one of our lockbox cash accounts.  Does anyone have advice on what to do with the open item in our lockbox cash account?  I thought about creating a second invoice to receive the "fake" customer payment then issuing a credit memo, but the credit memo would be a real credit to the customer account.

Here's the scenario:

1. Customer check was received via F-28 to clear customer invoice.

2. Customer check was then sent to our 3rd party lockbox processor and received a second time.  The same payment has now been received twice.

3. Customer invoice is now cleared with the first F-28 payment receipt.

4. We are left with an open item that is not real in our lockbox cash account.

Any advice on what to do with the open item is very much appreciated.

Thank you experts.

Dan