Is it possible to send SMS notifications without consent?

Question

API

There is an application Debts . I want to add a function to remind the debtor , send SMS not from the user, but from a third-party service. This is not advertising or mass mailing.
Is it possible to do so?
The numeric name is not important.
PS Cool if you know good services, I test additionally for Belarus-Ukraine, I did not find a universal worker.

Answer 1

that is, the creditor will send SMS to the debtor with his own hands through the application? then essentially it is no different from the normal direction of a text message.

Answer 2

smsc, smsru and others like them