Hi, i’m new to using this plug-in and also WP in general, but i had the same issue you are facing and the solution for me seems to be aligning “On-line booking available days” in Services and in Settings.
In the Services sections, I had Sat/Sun availability but in Settings section I had Mon-Sun availability. So when I would select Tue for example, it would give me that error that you had.
But once I aligned those two settings, then it worked.
It helped to have the option “Booking steps order” checked. That way it would show me only the days I set in the Services option. That gave me a clue that something was wrong.
Hope that helps
