Appearance> GeneratePress :Sorry, you are not allowed to access this page.

Dear Support,
I purchased the premium version of GP and installed according to the instructions given which said i should install as a plugin by uploading the downloaded zip file.
After that i activated successfully too.

But the challenge is that having done the activation, when i try to click on Apperance>Generatepress link to add license key, it display this error" Sorry, you are not allowed to access this page" Even when i try to check the installed themes, it is not among them on the list. Also it does not appear anywhere in the wordpress dashboard showing it has been installed.

Here is the site: http://supplies.digidats.com
WHat have i done wrongly? You kind advise will be highly appreciated.
I await your feedback in earnest.
santus