Installing Norton onto iMac

I'm installing Norton onto my iMac and kep getting stuck at "Kernel Extension" as its asking to select "Allow" but the 'Allow" button does not show. The result is a loop whereby ever time i start my iMac i get the same warning that Norton is not fully installed.

Actual error message is "Click Allow next to the Symatec message. If you dont see the Allow button then , click here to retry" when i click a iMac screen opens, but this screen (Security & Privacy) does not have an "Allow" button to select.