Hello there,
This issue is commonly caused by using Classic Teams, joining the meeting as a guest/external user, or organizational restrictions on the Polls (Microsoft Forms) app. Live polls work reliably only in New Microsoft Teams and may display but fail on submission in older clients or limited account contexts. Please check that you are running New Teams (Settings → About), try joining via the Teams web client as a test, and clear your Teams cache. If you joined as a guest, poll submissions may be restricted. For work accounts, your IT admin may also need to ensure the Polls/Microsoft Forms app is enabled for participants.
Thank you