Fatal Error When Activating Plugin

This is because you are running a True Themes theme that copied all of our code from All in One SEO Pack and used it in their theme without changing any names. You’ll need to contact True Themes as they are the ones that need to fix this.

Thats perfect work in flatsome theme.

This was actually a problem with your theme, which has now been fixed. Update to the latest version of the theme and it should work.

https://help.truethemes.net/knowledge-base/seo-module-updated-in-karma-4-8-0/