Hello,
Sorry for the issues you are having.
The license key is good for one install of WordPress and unfortunately, a production and a sandbox site is considered two installs. The plugin will work on both sites, but one will have to be manually updated.
All the details of our licenses can be found here:
Using one license for your live and dev sites
https://theeventscalendar.com/knowledgebase-category/purchase-install/
And if you want to change the license to another site follow these steps:
Try removing your license keys from your account on TheEventsCalendar.com and then reactivating them on your site to see if that resolves the issue.
To do that, login to your account and go to My Account > License Keys
Click “Disconnect now” next to all the urls and go to your site and add those license keys back.
Let me know how that works out for you.
Thanks