How to bill for services?

Question

Payment systems

I conditionally maintain the site on a monthly basis. The client paid me, I serve, a month has passed, the moment of payment has come again.
What are the options for arranging convenient payment without unnecessary reminders? Maybe some kind of contract that obliges the client to pay or something else.
It is desirable that this be as simplified as possible, without my special participation.

Answer 1

No contract will remind the client of timely payment.
Here, either an advance payment for some long period, for example, for six months or a year, will work, or you will have to remind him of the payment in advance.

Answer 2

payme.biz

Answer 3

The service issues invoices and reminds about payment
https://schet-na-oplatu.ru/