the short answer
Recurring billing for coaches is an automated subscription that charges a coaching client the same amount on the same date every cycle - weekly, four-weekly or monthly - without anyone sending an invoice. The client saves a card once at signup, agrees to a schedule, and the payment then runs on its own until it is cancelled. It is the standard way established online coaches collect money, because it makes revenue predictable and removes the monthly job of chasing payments. The alternative - invoicing each client by hand - leaks income the moment you have more than a handful of clients.