Are you sure the Dexcom credentials for logging in, didn’t change? Start by logging directly in to Dexcom and see if you see your BG numbers and live glucose data.
If you confirm the above to be good, see if SugarMate requires an update. If you have the most up to date app / version…
Re-authenticate through SugarMate. Log out completely, log back in. When prompted, re-connect / re-authorize Dexcom within SugarMate (make sure tou select the correct Dexcom region (US vs International)). Also, it has to be the Primary Dexcom account, not a follower account.
Then check system permissions.
On iPhone:
Settings → Cellular → make sure Sugarmate has data access
They recently changed the login process. I contacted tech support (support@sugarmate.io) and they were responsive and helpful. Come to find out that I was using an incorrect password on one of my sugarmate devices,