How to sync multiple devices to avoid double bookings in Appointments?

[HairLab]

I am a hairstylist and I use the appointments app for online booking as well as using my phone and/or an ipad in my studio to book through the app. Currently my ipad and phone are not synced and do not show the same appointment avalibility. This is causing chaos and allowing online bookings to be double booked with my appointment scheduler. This is no time of year to be having this issue, and truly it is just adding to the list of things making me want to move away from using this app in the first place. ive called twice to resolve this issue without any resolution to my problem and i have to continually call clients when they are double booking their appointments. PLEASE HELP!!