This article explains how you can void a single payment in Mangomint.
Note: This does not actually refund the actual payment. This step is to update your sales records and reports in Mangomint. If you are interested in that or how to handle refunds in general, please go to: Refunds
Select the sale in your Sales Screen
Click on the “...” button and choose the “Reopen” action which will allow you to modify the sale
Use the Go to Payments button to view the payments on the sale
Identify the payment that you want to mark as voided, click on the “...” button next to it, and choose “Void”
Once confirmed, the payment will show up as Voided within the sale.
Now select on the “back” arrow in the upper left to go back to the sale details