I see.
Please check schedule settings, Customer features settings and try to with the same parameters on public site.
If you have the same issue on public site please contact support, otherwise let us know, we will investigate issue further.
The schedule is all available. I am 100% sure because when we make two “book” API calls without add-ons it works. These issues are really annoying.
I cannot test this on the public site because our services have some location related issues. When it is clearly an issue in the API why can’t you guys take it up? Can you please ask your team to look into this in detail?
As i see the issue is repeatable on public site.
And as i see issue related to invalid configuration of “Appointment at fixed time” custom feature. Please disable it if you do not user it.