Step-by-Step Guide to Manual Activation of Unity
1. Start up your Unity Engine.
2a. (Windows) Click the Help tab and then click Enter serial number...
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2b. (Mac) Click the Unity tab and find the Enter serial number... drop-down.
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3. Click on Reactivate.
4. Select Manual Activation.
5. Click the Save License Request... button.
6. You will then have the option to save the .ilr file to your hard-drive.
7. Once you have the file saved, visit https://store-unity.unity3d.com/manual/. Upload the .ilr file generated in step 6, along with your Serial number for Unity. Click Activate Unity.
8. You should then receive a .ilf in return. Again, save this to your hard-drive.
9. Switching back to the Editor window, you should now click the Read License... button. You should then select the previously saved .ilf file.
10. Click Next. You're now active! \\