Trying to import license manually for offline device getting error license activation failed.

Hi,

Please check the article below to apply license in offline devices.
https://community.fortinet.com/t5/FortiGate/Technical-Tip-Procedure-to-apply-FortiGate-firewall-license-to/ta-p/198781

I had this same error as well.

The fix for me was to redownload the Offline license file. The original license file was slightly different from the license file I downloaded a couple days later.

This was on 7.2.6.