AWS exam shows "The check-in window for this exam is now closed."

I launched my exam on the exam day for AWS Solution architect associate - however it shows

"The check-in window for this exam is now closed."

I was not aware I could not reschedule less than 24hour before the exam, which I had done previously, but the system did allow me to reschedule.

I was wondering could this have been the case, why I could not take the exam?

Additionally, what can I do now? As the system should not have allowed me to re-schedule.

Thank you