Opt-in webhook is fired for several actions and is generally meant for binding a user in your application. This webhook is fired when:

Opt-in for Send to Messenger

When user presses Send to Messenger button, you will receive following webhook.

{
  "event": "opt_in",
  "timestamp": "2016-10-06T13:42:48Z",
  "data": {
    "channel": {
      "id": "6456078759331238786",
      "type": "facebook_messenger"
    },
    "contact": {
      "id": "6456078781510718339"
    },
    "opt_in": {
      "type": "send_to_messenger",
      "payload": "{{PASS_THROUGH_PARAM}}"
    }
  }
}

Parameter	Type	Description
opt_in.type	string	Describes what type of opt-in this is. In case of Send to Messenger, this will always be `send_to_messenger`.
opt_in.payload	string	Data set in Send to Messenger Button as `data-ref` attribute.

Opt-in for Checkbox

When user ticks Checkbox plugin, you will receive following webhook.

{
  "event": "opt_in",
  "timestamp": "2016-10-06T13:42:48Z",
  "data": {
    "channel": {
      "id": "6456078759331238786",
      "type": "facebook_messenger"
    },
    "contact": {
      "id": "6456078781510718339",
      "user_ref": "{{YOUR_CUSTOM_USER_REF}}" // set on frontend checkbox plugin
    },
    "opt_in": {
      "type": "checkbox",
      "payload": "{{PASS_THROUGH_PARAM}}"
    }
  }
}

Parameter	Type	Description
contact.user_ref	string	Data that has been set in checkbox plugin `user_ref` attribute. It is should be uniquely generated string ID (unique for each render).
opt_in.type	string	Describes what type of opt-in this is. In case of Checkbox plugin, this will always be `checkbox`.
opt_in.payload	string	Data that has been set in checkbox plugin `ref` attribute.

Opt-in for Phone Number Matching

This webhook is sent when a user accepts the message request sent to his phone number using Phone Number Entry Point.

{
  "event": "opt_in",
  "timestamp": "2016-10-06T13:42:48Z",
  "data": {
    "channel": {
      "id": "6456078759331238786",
      "type": "facebook_messenger"
    },
    "contact": {
      "id": "6456078781510718339",
      "phone_number": "15558576309"
    },
    "opt_in": {
      "type": "phone_number"
    }
  }
}

Parameter	Type	Description
contact.phone_number	string	Phone number in E.164 format.
opt_in.type	string	Describes what type of opt-in this is. In case of Phone Number Matching, this will always be `phone_number`.