Thanks for writing in!
Version 4.3 is using API key and the latest one is now using license codes (https://theme.co/changelog/#theme-x-4-4-0).
You may need to update the theme manually because 4.3 does not accept license code. You can download the latest version from your dashboard here: https://theme.co/apex/dashboard
To know how you can manually update the theme, please check out this knowledge base:
Hope this helps.