1. 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."

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