The balance is the contract
A session balance only moves when a session is actually delivered and marked. That single rule removes most client disputes, because the number both sides look at was produced the same way.
Solution
For a studio or an independent coach the unit of business is the session. Packs, balances, delivery and payout are one chain of records rather than a booking app plus a payment app plus a notes app.
Sell ten sessions, track the balance, expire them on your terms.
Availability, bookings and reschedules with a cancellation window.
Workout plans and exercise libraries assigned per client.
Measurements, photos and performance over time.
Diet plans and adherence alongside training.
Trainer earnings computed from delivered sessions.
A session balance only moves when a session is actually delivered and marked. That single rule removes most client disputes, because the number both sides look at was produced the same way.