I would recommend you to contact the support of the generate press and ask them to whitelist your server’s IP. If they recommend anything to be done from our side then feel free to ask us anytime.
I logged in but didn’t see the Secondary API code.
So I installed the Code Snippet plugin and added the Secondary API code, tried to activate the license key and it worked immediately. https://www.screencast.com/t/6EGyUImN
I think your server support didn’t actually install that code for you.