Cannot book anymore

Hello,
When we have a client that booked, and then later is canceled. so in the system shows the booking is canceled.

Then another client wants to book that same time which is available now again. gets an error with time slot is unavailable…
But is able to selected just not te place the service.

The error we get in the console: Failed to load resource: the server responded with a status of 500 ()

Looks like something broke with the last update that you guys did with certain code in your plugin.
https://linhsannagelstudio.nl/boek/

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