Sending messages on behalf of a user?

Question

API

Went through the documentation. REST methods are all basically about getting some kind of information. I didn’t understand whether there is an opportunity to write, comment, respond on behalf of the user using access_token. And it’s also not entirely clear in principle how to work with messages, whether there are webhooks, how to keep track of what has been read, what has not been read, to see new received messages, etc.
Thank you!
PS: On the site they did not find a normal form to ask this.