This could be one of two things:
- If you purchased a "Hobbyist" license, be sure you've not activated your license on more than 2 sites simultaneously. If you purchased a "Hardcore" license with unlimited installed, this should not be an issue.
- Typically, when your API key fails to activate, it's due to your hosting provider's server configuration not allowing your site to reach out and check the status of your license. Contact your hosting provider and have them check the error logs of your site to see if "outgoing curl requests" are disabled. Enabling these requests should correct the issue.
If you continue to have issues, please create a ticket with all the necessary info and we'll be happy to help.