It is not possible to finalize a Ticket Upgrade when the new total ticket price is equal to the total value of ticket(s) that you want to upgrade. In this case, you can place a new order in the regular ticket shop (find more information here). 

Next to that, it is not possible to finalize an upgrade when the new total ticket price is lower than the total value of ticket(s) that you want to upgrade. In this case, please contact the event organizer if you have questions regarding this case.