Base Membership - Some membership like 'Personal Training' may require a base membership of 'Gym member' to be valid to enjoy the PT. In this case 'Gym membership' is called as the base membership for 'Personal Training' and can be configured in the system at the Product Type configuration
At the time of Add-on Purchase - if the member tries to purchase an add-on membership without having the valid required base membership the system will stop the transaction show and error specifying that the required base membership is not valid or not found
Similarly FitnessForce system will also validates the Base membership validity at the time of consumption e.g. When a Personal Training session is being conducted and at the time of marking the members session attendance and the base membership is not valid then system will throw similar error.
At time of Booking - However if the base membership does not exists then at the time of booking it self system should stop from Booking the appointment.