While doing register close you may find Open Tickets, they are orange highlighted, when this happens, the save button is disabled.
To check if you have Open Tickets, you must go to: Sales Screen (Map Screen) > Menu > Register > Unsettled (open) Tickets which are on the lower right side of them screen.
To Close the Open Tickets, you need to check the open ticket from Sales (or map) screen > TICKETS section and close via paying the tickets.
Press TICKETS and you will see all open tickets which have not been closed.
You may use the PAY function to pay for the ticket on the spot.
After closing all the open tickets, you'll be able to do the register close.
The link about this feature: https://docv2.veronapos.com/operation/register-open-close/register-close-open-tickets