"Fatal Error 'OAuth\Common\Storage\Session' not found" when trying to connect to connect to Google or Vimeo
Hey Daniel and sorry for the lack of response. Please get in touch at ben@dukt.net and I'll be happy to offer you the license hoping you'll accept my apologies for the huge delay in my reply.

Regarding your issue, it looks like some classes haven't been loaded (OAuth\Common\Storage\Session). Can you please check if Session.php file is present in OAuth plugin's folder under oauth/vendor/lusitanian/oauth/src/OAuth/Common/Storage.

Also, you might consider get a fresh copy of the latest release of the OAuth plugin and try to unzip/re-upload the files, I'm thinking you may just have some missing files and that could fix the problem, otherwise we'll dig further.