I uploaded the downloaded GP Premium folder via FTP, as plugin upload within WP did not work.
I can see it now in the plugin list, but when I click on “activate” i get the message, that is was not possible to activate due to a fatal error
Warning: require(/homepages/17/d371486983/htdocs/app450182430/wp-content/plugins/gp-premium/inc/activation.php): failed to open stream: No such file or directory in /homepages/17/d371486983/htdocs/app450182430/wp-content/plugins/gp-premium/gp-premium.php on line 15
Ok, that was the point, there was no inc folder at all, only the folders with the first addons I bought at the beginning. I downloaded the GP-Premium.zip now again and it has the complete content now. Now activtion worked, thanks for your help! 🙂