I experience the same problem. I also get the error
changes: Cannot create an abstract class,
I am using a customer that I just created (which also shows in the list of customers), so an invalid customer is not the case here. Max attendees is set to 1, so these conditions are not in place, but the customer does exist.
Any help would be highly appreciated.
I am investigating whether the MS Bookings api (part of Graph) would be something we can use. Since this is not the only issue I ran into, I have my doubts...