Using odoo.sh 15

Today a customer had a problem with his card and he was allowed to pay later with bank transfer.  Problem is that the payment was allready booked in the pos system, we allready printed the receipt.  

On his invoice it marked payed, incorrect, so i had the luminous idea to delete his payment, so that i would appear correct to the customer.  

Now i can not close my pos session.  Whatever i do i get errors.  

Right now i am going back and forth between:  

Some tills are already booked. Reset them to new to close the session.
Cash registers: ['POS/00127'] (google translate from :  Sommige kassa's zijn al geboekt. Stel ze opnieuw in op nieuw om de sessie te sluiten. Kassa's: ['POS/00127'] )

But when i reset the cash booking to new i get:

You can only reconcile booked bookings. (google translate from 
Je kunt alleen geboekte boekingen afletteren.)

Please help me to fix this, i need to be able to start a new session in a few hours.