If you've manually added a payment to an invoice using the steps outlined in the Mark an Invoice as Fully Paid or Mark an Invoice as Partially Paid articles, and you need to remove that payment for any reason (e.g., you refunded a cash payment, marked an incorrect amount as paid, etc.), you can do so using the following steps:

iOS and Android

1. Tap Invoices and open the invoice you would like to remove a payment from 
2. Tap Transaction history
3. Tap on the payment you wish to remove
4. Tap Delete payment
5. Tap Yes-delete

Web

1. Click on Invoices from the side navigation menu and open the invoice you would like to remove a payment from
2. Click on View transaction history
3. Click on the caret 'v' next to the payment you wish to remove 
4. Click on Delete
5. Click on Delete again

Please note that you can't undo this action.