Coupon on first, all and... Intermediate number of payment

Hi Dear,

I think it could be useful for the coupon have the possibility to work on not only on firt or all payment, but also "intermediate" numbers of payments.


E.g.

Plan A - 50 $ / month

Coupon A - 50 % (or 25 $)
Number of payment: 1, 2, 3, 4 ... nn, All


Very thanks