If you see Unable to Activate Tag while trying to activate your CGM device, it is possible that the tag is already active.
Try scanning the sensor by pressing the + button on the dashboard and selecting Scan from the menu. If the scan succeeds, then the sensor is already active.
If the scan was not successful, make sure when you are trying to activate the sensor that you are bringing the area of your phone where the NFC is located to the sensor.
If the sensor continues to give you trouble while activating, try running through these troubleshooting flows for your respective device: