Atm it's not possible to move any position with a value of 0 to an open bill. Since we customize our bills in another way as Mews usually does, we need to move all reservation items to an open bill. This way we can pay all reservation items, close the bill, checkout the reservation and receive a pdf in the end.

Some of our hotels place 0 value positions on their reservations as reminders. Atm it's not possible to checkout those reservations, since not all reservation items get on the same bill and therefore we cannot "pay" all reservation items.

So there are two different solutions:
1.) Make it possible to move those 0 value positions to an open bill
2.) Make it possible to checkout reservations with an open amount of 0.