Hi Katelyn,
Thanks for taking the time to reach out to us here! This error message is most commonly seen when attempting to move your existing license key from a development/staging site to a live site or when the server for your existing site has otherwise changed. If you need to clear a previous activation for your license key, you can do this right from your account on TheEventsCalendar.com:
https://theeventscalendar.com/knowledgebase/moving-your-license-keys/
Once you’ve removed the activation for your development site, you’ll be able to activate this key again on your live site. Let us know if you should have any questions or concerns as you’re working through the steps here! 🙂
Cheers, and thanks again!