Use the "Quick Find" field from the Setup menu to search for ”sites” or manually navigate to (Setup -> App Setup -> Develop -> Sites)
2) Copy or make note of the ”Site URL" for your GetAccept Callbacks Site.
3) Open a new browser window and paste in the url adding "services/apexrest/gaff/getacceptcallback/" at the end (make sure to include a / at the end of the URL).
4) If GetAccept Callback configuration is valid, message on screen should be "GetAccept OK."
