Я понял, на всякий случай, если кто-то еще попытается сделать то же самое и застрянет:
to = ChannelAccount(id=to_user_id)
bot_channel = ChannelAccount(id=bot_id)
activity_reply = Activity(type=ActivityTypes.message, channel_id='msteams',from_property=bot_channel,recipient=to,text=message)
credentials=MicrosoftAppCredentials(app_id, app_password)
JwtTokenValidation.authenticate_request(activity_reply, "Authorization", credentials)
# That's where you pass the tenant id
reply_conversation_params=ConversationParameters(bot=bot_channel, members=[to], activity=activity_reply, channel_data={ 'tenant': { 'id': tenant_id } })
connector = ConnectorClient(credentials, base_url='https://smba.trafficmanager.net/uk/')
# Create conversation
conversation = connector.conversations.create_conversation(reply_conversation_params)
# And send it
connector.conversations.send_to_conversation(conversation.id, activity_reply)