You might see this error if you entered an invalid product key or a product key for a different version of Windows. Enter a valid product key that matches the version and edition of Windows 10 installed on your device. You may try these steps below:

1. Click on the Troubleshoot tool at the bottom of the error message. 

2. Restart and/or update your computer, then enter the 25-digit activation key.

NOTE: If the steps above didn't resolve it and you're still getting an error, please open a new support ticket  and include the following details below so we can assist you better: 

1. Order / Transaction ID

2. PayPal email address and/or Delivery email address (if different from PayPal email address)

3. Type manually the product key (code or pre-loaded account details)

4. Screenshot of the pop-up/error message

5. Additional information (if any)