In the new Patient Payments system, you can delete payments that were entered in error. To do so, you'll need the "Billing Administrator" and "Access Patient Payments" permissions checked off. If you are a practice admin, make sure you have these permissions checked off for any Staff Members who will need to delete payments. (How to set Staff Permissions)
With "Billing Administrator" and "Access Patient Payments" enabled, go to Billing > Patient Payments (Beta).
Click on the "Payments" tab in the top left corner, then search for the patient you need and "Update."
You can then click the Lock Icon on the left side of the screen to enter "Unlock Mode." You'll get a pop up asking "Are you sure?" to which you can reply "OK."
Once in unlock mode, you can identify the payment which needs to be deleted, and click the red X icon to the right of that payment. The system will ask you to confirm the deletion, and after doing so, the payment will be deleted altogether.