How to create a telegram channel / chat / bot analogue of a bulletin board?

Question

API

Terms of reference - the user logs in to the site through the telegram widget, or bot, fills out the ad form (roughly speaking, we have a telegram user ID and ad text) and it is published in the channel / chat / bot. The problem is how to organize the connection of participants with the author of the ad, given that not everyone has a username, and forcing them to fill in this field is not user friendly?

Have experience with Telegram Bot API