I am going to try and explain this the best I can.

Scenario as an example:

I offer 5 personal training sessions and my client has 3 months to use them all. If she only uses 3 in the first month she only as 2 sessions left to use in the remaining 2 months.

The way trainerize is set up, is the sessions reset after each month. So if I set the expire to 3 months, her "5 sessions" reset after the first month to another 5 and she only purchased "5" so she shouldn't get more.

I find some of my clients need a longer time to be able to complete all their sessions they purchased and I do not want them to reset after each month.

The payment plan option is PERFECT, but it needs to be separate from the sessions expiry. As I still want my client to be able to make payments towards her sessions but NOT the same length of time as when her sessions expire.

5 sessions purchased total cost ($500.00)
$100.00 payments for 5 weeks
All 5 sessions purchased expire within 3 months. (if she doesn't use the 5 sessions in the 3 month timeframe, they lose them)