Trouble shooting
#1. Is the Call back URL correct? Make sure
you are using the RIGHT callback from your bullet response account..
Projects > Choose your FanPage > Action > Call Back.
#2. Is the Page Subscribed on Facebook App ?
#3. Make sure ONLY pages_messaging is selected.
If you see pages_messaging_phone_number then DELETE it.
All you need is pages_messaging
#4. Did you watch the webinar training? If no,
see this : https://www.youtube.com/watch?v=J9434v096zM
It will 100% help.