In order to change payment method you dont have to inverse the invoice. You can do that directly with the already created invoice.

  • Go to POS
  • Click on the spy glass right next to "Order No:"
  • Find the invoice
  • Double-click on it in order to display it in POS
  • Click on "OK" when you see the "Validation" message
  • Click on "F4 Invoice"
  • Click "OK" when you see the "Validation" message
  • In order to delete the payment click on the red "X" signt right next to the "$" signt
  • Choose "Yes" on the "Validation" and "Warning" messages
  • Choose new payment method