Ask HN: A payment processor that pre-charges metered use

My example would be a music school: students pay by credit card or cash on the 1st of each month for the number of lessons they are scheduled to receive that month. For example, in October, someone who has lessons on Wednesday will have 4 lessons and be billed $40 on October 1st, but that same student will be billed for 5 lessons on November 1st because there are 5 Wednesdays that month.

Stripe and PayPal don't seem to have this ability (either pay afterwards, or it must be the same amount each month).

Is there a processor (ideally as easy to work with as Stripe) that supports this type of billing?

Thanks HN!