Automatic update is unavailable for this plugin.

I've read through several similar posts to mine to no avail. I installed the wpForo Advanced Attachments and it's working great. No problems. However, I keep getting this message, "Automatic update is unavailable for this plugin.To receive automatic updates license activation is required. Please visit settings page to activate your plugin."

I cannot locate my activation key. I bought your product only days ago, but checked out as a guest. Since then, I also purchased Private Messages, and registered, so my account only shows that purchase. 

Your help is greatly appreciated. Thanks.