I have an issue with the invoice payment and I can't seem to find what is wrong with it....

When I use their online demo everything goes fine... I add a customer, then create an order verify it etc and then register a payment

when I enter for example the full amount there is no option for the invoice to remain open and it goes to paid

On the other hand on my installations (both lixun and windows) everytime I try to do the same thing

It keeps having the keep open and no matter how much money I put in it says that amount is the difference

what am I not getting ?