Please check that
- You tap on the "ACTIVATE APP" button after you've cleared Singapore’s immigration, i.e. after your passport is "stamped"/processed at the Singapore checkpoint, and
- The details that you entered into the app match the Passport that you used to enter Singapore.
If you've just cleared Singapore's immigration, there may be a short time lag (2-3 mins) before you can activate the app.
If you continue to face issues activating your App, please email support@tracetogether.gov.sg with your query and details of the issue you are facing.