Hi Dugson,
I’d be happy to help you out with this!
I took a look at your system info (thanks for sending that!), and it doesn’t look like you have Events Calendar Pro active. The space to enter your Pro key under Events > Settings > Licenses will not appear until the plugin is activated – can you try activating it and see if you see the box?
The space that appears there by default is actually for Event Aggregator, which is an import service that is built into the free version. It sounds like this might be where you entered the Pro key?
Let me know if activating Pro and entering the license in that box gets rid of that message!
Thanks,
Jennifer