Personal notification service for users?

Question

Messengers

Good afternoon.
Can you tell me the services through which you can send notifications to messengers?
Those. the user clicks on the site on the telgram or whatsapp icon, thereby subscribing to notifications.
The script from the site sends a notification to a specific user, which reports information about attending the event to which he subscribed.
It's good that it would be possible to communicate with the client through a bot / service.
Thank you.

Answer 1

vatsap does not have such an opportunity so far
here we have described a scenario of how to send a notification to a vatsap for a user
https://molotok-studio.ru/blog/kak-podruzhit-bitri...
but further communication still goes through the messenger itself, so you just get his contact