I see the error 'Your serial number is not valid’ when attempting to activate through the Unity Hub. What does this mean?

Symptoms:

• I want to activate my license via the Unity Hub. However, I am receiving errors.
• My serial number/ license key is not activating.
• I see the error message 'Your serial number is invalid' when attempting to use Unity.
• I see the error message, 'Serial number has reached maximum license activations'.
• I see the error message, 'Your serial number is not valid' when attempting to use Unity.
• I want to access the Unity Editor, but I am receiving errors in the Hub.
• The Hub is saying my serial key is invalid.

Cause:

The most common cause for this error is that the license/ serial key has run out of activations. If you have recently updated your OS or changed any hardware, this can alter the hardware ID to which the Unity License File (.ULF) is attached, effectively making the current .ULF redundant. 

Another cause for the error 'Your serial number is not valid' is a connection issue between your machine and the Unity license servers. 

A previous license file is blocking the creation of a new one.

Resolution:

You can return activations made in Unity Editor versions 4.5 and higher via your account page. To do this, see the article 'How do I return the activations on my Pro/ Plus/ Enterprise license?'.

If you still receive an error after completing the above process, then the error is likely caused by a connection issue between your machine and our license servers. In this case, please check any firewall/ proxy settings, safelist URLs, and disable any antivirus software.

Failing that, manually activating would be the next process to follow. Please see the article, 'How can I manually activate my license inside the hub?'.

If releasing your activations & checking your connection still does not help you activate your license, you may be experiencing a conflict with the license file saved on your machine. You need to delete the existing license file and create a new one:

1. Close the Hub completely using the task manager or similar.
2. Using your file explorer, navigate to;
   • Windows: C:ProgramData/Unity
   • Mac: Library/Application Support/Unity
     and delete the .ulf file housed there.
3. Launch the Hub again, ensuring you allow the Hub to make changes to your hard drive in the process.
4. Reactivate your license following the steps outlined in the article, 'How do I activate my license?

If your license is still not activating after troubleshooting the above, please get in touch with Customer Experience with your Hub log file so we can take a closer look at your issue. 

More information:

I have been asked to provide a log file, where do I find this?
How do I activate my license?
Manual activation guide
How do I return the activations on my Pro/ Plus/ Enterprise license?