Hello, @Fernez,
I have checked your site now and found that the issue appears because your server requirement does not meet the theme and plugin requirements. So In order to solve your issue please contact your service provider and ask them to set server requirements to meet the theme requirements. See the image for the theme requirement here: https://ibb.co/VBscvWg
And then Please try to deactivate and then reactivate the theme again with the same purchase code and then try to import the demo on your site. I hope your issue will be resolved.
And I can see you have purchased 2 licenses and both have been used on the sites, so according to the ThemeForest license policy, you can use 1 license for 1 project only (dev site, production site, localhost but the same project), read more – https://themeforest.net/licenses/terms/regular If you want to use our theme for a few different projects you need to buy a few licenses.
Regards 8Themes Team.