Do you have an overpayment that's not applying to an unpaid invoice?
Here are the steps to apply it.
1. We want to record the details of the overpayment (such as type, amount, etc) and then delete the overpayment. 
2. Once it has been deleted we have to re-enter the overpayment and apply it to the necessary invoice.
3. On the payments page, select "Add New Payment"
4. Select the Customer
5. Go through the process of adding a payment like you normally would. Make sure you re-enter the FULL amount of the overpayment.
6. Once you've entered the payment information it will give you the option to apply it to the unpaid invoice.
In this case our overpayment is for more than the invoice amount, so they system alerts us that we will still have a remaining overpayment.
7. Once you've completed the payment process and saved it, we can go back to the Customer Dashboard under Invoices and Payments and confirm that the overpayment was applied.
As seen below, all the invoices are now marked as paid and our remaining overpayment is listed.
We hope this helps! Please reach out if you have any further questions at (951) 234 5166 or email us at support@paythepoolman.com