Cannot create booking events in the same month

Problem/Motivation

Getting the error message on the attached image when trying to book more than one hourly event on the same month.

Steps to reproduce

- Install BAT
- Install BEE
- Set to entity flexible
- Set availability hours
- Create a reservation
- Create a reservation within the same month of the first reservation

Proposed resolution

Change the primary keys of the tables.
I suggest simplifying: an event ID column autoincrement for the event tables and a state ID column autoincrement for the state tables