Defender for IOT Activation file is not valid

The message "This activation file is not valid" indicates that the OT sensor is rejecting the activation file, typically because it does not match the sensor’s current registration or has expired.

To resolve this for a locally managed OT sensor with an on-premises management console:

1. Reactivate the sensor from the Azure side
   1. In Defender for IoT in the Azure portal, go to Sites and sensors.
   2. Delete the existing OT sensor entry that corresponds to this appliance.
   3. Onboard the sensor again, registering it with the correct settings (management mode, site, plan commitment, etc.). For details, see the onboarding steps in Onboard OT sensors.
   4. As part of onboarding, download a new activation file for this sensor.
2. Upload the new activation file to the sensor
   1. Sign in to the OT sensor console.
   2. Go to System Settings > Sensor management > Subscription & Activation Mode.
   3. Select Upload, choose the newly downloaded activation file, then select Activate.
3. Check for common causes if the error persists
   • Expired activation file: Activation files expire 14 days after creation. If the file was generated earlier and not used in time, download a fresh activation file from the Sites and sensors page and repeat the upload.
   • Connectivity issues: If the sensor cannot communicate with Azure during activation (for cloud-connected mode), verify network configuration, proxy settings, and that required endpoints are allowed. For OT sensors version 22.x, endpoint details can be downloaded from Sites and sensors > More actions > Download endpoint details; for earlier versions, see the networking requirements. For newer versions, ensure equivalent connectivity requirements are met.
   • Pending activation/reactivation state: If the sensor health shows Pending activation or Pending reactivation, upload the correct activation file again and verify the sensor can reach Azure.

If a newly generated activation file is still rejected after these steps, the guidance is to download another activation file from the Azure portal and, if that also fails, open a case with Microsoft Support.

References:

• Maintain OT network sensors from the sensor console
• Manage sensors with Defender for IoT in the Azure portal
• Sensor health message reference
• Configure and activate your OT sensor
• What's new archive for in Microsoft Defender for IoT for organizations