Do you thing you have duplicate Customer payments posting???
You probably don't have duplicate payments, just payments that need to be matched.
If you posted a payment that is still pending in undeposited funds
then go to the Bank register and double click the deposit to open it.
Click the Payment Icon and choose the payments that need to be listed in
the deposit. Then click on the original deposit entry line(s) and
choose the Edit drop down list and choose Delete line. This will post
the undeposited funds entries into the deposit correctly and will not
affect the reconciled status of the deposit.