A Payment Agreement will explain to your client how and when payments are due and how long sessions purchased in advance will be valid for. No-one likes to ask for money, so a payment agreement makes it clear from the outset when payment is due.
I ensure that sessions are paid for one session in advance to cover no-shows. I set the validity of sessions paid in advance to 90 days; this prevents clients with unused sessions calling you in 3 years time asking for their unused sessions to be refunded. Make sure you document the sessions that are paid for by your clients to keep track of payments and the funds on your clients account; there’s a template for this in the Personal Trainer Business Forms and Templates pack.
You can find a Payment Agreement template in the Personal Trainer Business Forms and Templates pack for you to customise to your needs.