I just stumbeld upon this. I did the steps as mentioned above (https://forums.unraid.net/topic/92245-telegram-bot-notifications/#findComment-963072).
After that the test routine did not run at first. I tried to recieve my "chat id" and was ready to make some manual changes. The retrieval of the chat id did not work, the json was empty, so I did send my bot some messages. This resulted in a working id retrieval but also resulted in a working test procedure from unraid without further steps or manual interventions.
I am running Unraid 7.0.0-rc2
tl;dr
send your bot a few messages an try test routine again, no guarantees