The customer has made an advance payment, but my employee recorded it against an invoice. What should I do to correct this?

1. Go to the Sales module and select Invoices.
2. Click the Payments Received section on the Invoice Overview page and click the Delete icon.
3. On the Delete Recorded Payment page, choose the Dissociate & Add as Credit option.
4. On the following page, click Dissociate & Add as Credit.

Now, this payment will be stored as credit for the customer.