Ah I see, you are using the unofficial notifications plugin, not the ‘chat-integration’ plugin? The “Ask an administrator to add a channel with” message you shared above looks like the chat-integration plugin 
If you really are using the notifications plugin:
Are you replying directly to the messages in telegram? (on iOS, long press on the message, then click reply)
Are you trying to use the notifications bot in a group chat/channel? That is unlikely to work.