This message displays when the cashier is trying to process a transaction using more than amount total displayed on the point of sale terminal using the selected payment method. To stop this popup, you will need to allow that payment method to process more than the total. Go to the payment methods screen by navigating to Settings > Payment Methods.
Select the payment method you need to make the change to and click on the edit button. Once you are inside the payment method edit screen, tick the “change due” checkbox. Click on save. Make sure you retrieve master data on all points of sale terminals that are using that payment method. You will now be able to process amounts greater than the total receipt for that payment method.