User not able to see anything (Error), when Bot Service returns status code 403 about botbuilder-microsoftteams HOT 1 CLOSED

This is a really good suggestion. The challenge is that the topology of message delivery is quite different across emulator, web chat, and Teams. When the user sends a message to the bot, our bot message service accepts it and responds with 200 OK. The message then fans out to the actual recipients later, so the 403 that you return is not fanned out to the recipients. We would have to change that logic to honor it, in effect generating a system-generated message in response to any bot message.

We've added a feature to the backlog to track this, but in all honesty you are the first to report this and until we hear about this from more developers, we likely won't get to this in a while. It requires a change on all our front end clients as well as the service side, because in effect this requires us to say "OK, user message received" but then change it later to "oops, this didn't go through, would you like to retry?" like web chat and the emulator do.

from botbuilder-microsoftteams.