The goal of the flow is to prevent double cooking if the category has been assigned for the day (no need to check time) of the calendar. This is what I have so far. If the category is chosen, do not save the item, send email about the double booking.
So for example, April 10, 2019, Category = Meeting then someone trying to book again for the same day and trying to choose Category = meeting, do not save, send email.

Thanks for the help.