Can't activate serial key - legacy activation method

If you're trying to activate an old license using the legacy serial key method and getting the error 'The serial number (xxx) is not valid for this product', the most likely cause is that you're using the license ID and not the serial key.

Serial keys look like this: 123-456-123456-1234.

With user account licensing you don't need your serial key to activate your license, you can activate by logging in with your Redgate ID and this ensures that you never run out of activations. On the toolbar of the tool, click on Help > Manage my license. 

If you're activating on a machine without an internet connection you will need your serial key. To view your serial key click on Licenses and turn off the new licensing experience:

Click on the product tile, then the Serial Numbers tab: