Why is a time slot not available in online booking?

Check in this order

1. Verify that the shop is open on that day and at that time.
2. Verify that at least one active employee is working then.
3. Verify that the employee has the selected treatment as an active skill.
4. Check holidays and one-off schedule exceptions.
5. Check whether the selected duration and required buffer fit completely inside the free period.
6. Check the minimum hours in advance, bookable days ahead and the block after opening.
7. Verify that the treatment type is active and has a valid price for the selected duration.

Then test the booking widget again with exactly the same treatment, duration and date as the client.

An admin can schedule manually outside opening hours, but those times are not automatically offered to clients.