Questions to answer first.
THE BASICS
What the customer gets each period The price and interval When billing starts What happens when payment fails What happens on cancellation Whether you offer refunds
WHAT HAPPENS ON CANCELLATION
Access ends immediately, or at the end of the paid period?
The second is fairer and standard.
State it.
WHAT HAPPENS ON FAILED PAYMENT
Retries, for how long, with what notification, before access ends.
REFUNDS
For a monthly subscription, most businesses do not refund part-months.
Whatever you decide, state it.
UPGRADES AND DOWNGRADES
Can a customer change tier, and when does it take effect?
Prorated or at the next renewal?
PAUSING
Some businesses allow it. It reduces cancellations.
Decide whether you will.
WHAT TO WRITE DOWN
All of it, in your terms, before taking a single payment.