Hello Sahil,
That might be because you are attempting to install a theme and activate a plugin on a website that has already been built with other themes. This could be the cause of the conflict, or it could be due to a third-party plugin. We suggest that you try to install the theme on a fresh WordPress installation. We are confident that you will not experience this issue again.
If you do, please provide us with the fresh WordPress admin URL and credentials in the private content area of this topic, so that we can install the theme and core plugin for you on your site.
Best Regards,
8Theme’s Team