Cant pick date

Hi,

we got a problem, it worked until now, but do not know what happened.
On this page: https://gokartarena.hu/palyafoglalas/ if you click “Foglalok” button the booking interface comes in, but I can’t choose other date, only today.

What happened?

Thank you in advance.

The page I need help with: [log in to see the link]