Below is a helpful checklist to go through if you are having issues
Please note that before your messenger bot is allowed to be used by the public, your app must first be submitted and accepted by Facebook. Once it is approved, anyone can interact with it by clicking on the Call to Action button you created on your Facebook Page.
Have you correctly added your Facebook Page ID?
Have you double checked to make sure that your Facebook Page Access Token is correct?
Are you the Facebook App’s Administrator?
If you created the app yourself, you most likely are. To be sure, go to developers.facebook.com and select your app from the drop-down section. Click the Roles section from the menu on the left hand side. If you are an administrator, you will be listed at the top under the Administrators section.
Not an admin, but still need to test a messenger bot?
Not a problem, just have whoever is the admin of the app add you under the Testers section in Roles. They can easily add you by Name, Facebook ID, or by Username.