Ebayomatic – unable to contact plugin API endpoint

Hi, I've just purchased the ebayomatic plugin and going trough the setup options. The tutorial video / docs don't include any information regarding the API keys configuration (not good!). I've created a production auto token as ebay dev, however I'm unable to set the Ebay Cert ID until the ebay API successfully sends a test notification to the plugin endpoint. I have setup the closure end point URL correctly within ebay and created a verification token which matches inside the plugin and ebay. Is there any useful documentation/logging to investigate the issue?