Example callback events in the Dropbox Fax API

Updated Sep 26, 2025

POST /callback.php?type=outbound HTTP/1.1
Host: your.callbackdomain.here
Accept: */*
Expect: 100-continue
Content-Type: multipart/form-data; boundary=---------------------------e2bdba1d3cf0
Content-Length: 520
X-Forwarded-For: 52.200.252.64

------------------------------e2bdba1d3cf0
Content-Disposition: form-data; name="json"

{"Transaction":{"Guid":"[Fax GUID]","To":"14154847140","From":"14154847140","IsInbound":false,"IsDraft":false,"TypeCode":"F","StatusCode":"S","ErrorCode":null,"CreatedAt":"1505933982","UpdatedAt":"1505934022","Uri":"\/v1\/Accounts\/[Your Account GUID]\/Transmissions\/[Fax GUID]","NumPagesBilled":1}}
------------------------------e2bdba1d3cf0--

Learn how to send a fax using the Dropbox Fax API.

Here is an example of a callback process for an outbound fax with an error. In this case, it's a bad Recipient Fax Number:

{
   "Transaction":{
      "Guid":"[Fax GUID]",
      "To":"1214155555555",
      "From":"14155555555",
      "IsInbound":false,
      "IsDraft":false,
      "TypeCode":"F",
      "StatusCode":"E",
      "ErrorCode":"A",
      "CreatedAt":"1475766509",
      "UpdatedAt":"1475766550",
      "Uri":"\\/v1\\/Accounts\\/[Your Account GUID]\\/Transmissions\\/[Fax GUID]",
      "NumPagesBilled":0
   }
}

Note: We are aware of an issue where, if you have an Account Callback URL profiled in the hellosign.com API Settings page, you'll receive Dropbox Fax events similar to the even shown below.

{
   "event":{
      "event_type":"transmission_disconnected",
      "event_time":"1475766511",
      "event_hash":"9a306f1874007d9f40f946e21480dcb9a1688516776cbea6f471c4c1e0db1502",
      "event_metadata":{
         "related_signature_id":null,
         "reported_for_account_id":"[Your Account GUID]",
         "reported_for_app_id":null,
         "event_message":null
      }
   },
   "account_guid":"[Your Account GUID]",
   "client_id":null,
   "transmission":{
      "test_mode":false,
      "title":"fillable w9 test doc",
      "original_title":"fillable w9 test doc",
      "subject":null,
      "message":null,
      "metadata":{

      },
      "from":"1415555555",
      "transmissions":[
         {
            "status_code":"error_disconnected",
            "recipient":"12141555555"
         }
      ],
      "transmission_id":"[Transmission GUID - Different than Fax GUID]",
      "final_copy_uri":"\\/v3\\/transmission\\/final_copy\\/[Transmission GUID - Different than Fax GUID]",
      "files_url":"https:\\/\\/api.hellofax.com\\/v3\\/transmission\\/files\\/[Transmission GUID - Different than Fax GUID]"
   }
}

You can choose to parse or ignore these events as needed - they're not strictly required. The Dropbox Fax callback Transaction is the one that's explicitly regarding the Dropbox Fax faxing attempt.

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