Add Plugins' button missing from Sub Site Menu

Hi there

I am installing my first MU site and have added a sub site under the main domain and am getting ready to add supporter plugin

I have activated admin options to see installed plugins and also network activated plugins as required.

Th issue I have is that even though I can see the Plugins Menu Item in the sub site and can activate individual plugins that I installed at the network admin domain I cannot Add any new plugins for that site from the Sub Site

Any help please