The prefill amount is one of the coolest features in Odoo13 POS. The payment input will behave similarly to bank payment input, we can speed up our billing and by using prefill we can make our payment without mistake, the amount will be automatically filled to the space of amount and we can edit it too. And will be prefilled with the exact due amount.for that you have to enable the option to prefill in our session settings, then only you can use the function and if you don,t want to use this function just disable it, but you can change it only when close and validate the session that means we can't make change to the option will the session is on progress or running. This video will explain the use of prefilling how it work on odoo 13