The Arnio API follows REST principles. You can use it to send outbound iMessages globally.

Supported Endpoints

Single message: POST /send-message
Group message: POST /send-group-message

Sending Files

You can send media by including the media_url parameter.

The URL must point to a publicly accessible image or .caf (for voice notes).
File size is capped at 5MB.
Signed URLs are not supported; use Arnio’s media object pattern for secure uploads.

Learn more here: https://docs.arnio.co/api-reference/endpoint/send-message

Status Callbacks

Arnio will POST to your status_callback endpoint when a message’s status changes. Possible statuses:

QUEUED
SENT
DELIVERED (iMessage only)
READ (iMessage only)
FAILED

You must respond to Arnio’s webhook to prevent duplicate notifications.

{
  "accountEmail": "support@arnio.co",
  "content": "Hello world!",
  "is_outbound": true,
  "status": "DELIVERED",
  "error_code": null,
  "error_message": null,
  "message_handle": "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxx",
  "date_sent": "2025-09-10T06:15:05.962Z",
  "date_updated": "2025-09-10T06:15:14.115Z",
  "from_number": "+15122164639",
  "number": "+19998887777",
  "to_number": "+19998887777",
  "was_downgraded": false,
  "plan": "enterprise"
}

Note: Your server must return a response to Arnio’s callback to prevent duplicate webhook deliveries.

Callback Body Fields

Field	Type	Description
accountEmail	string	Associated Arnio account email
content	string	Message content
is_outbound	boolean	true if sent by your system, false if received from end user
media_url	string	A CDN link to any attached media
status	string	Current status of the message
error_code	int	Error code if the message failed, null otherwise
error_message	string	Human-readable error description
message_handle	string	Unique Arnio message handle (used to query message status later)
date_sent	string	ISO 8601 timestamp of when the message was created
date_updated	string	ISO 8601 timestamp of the last status update
from_number	string	E.164-formatted Arnio phone number used to send the message
number	string	E.164-formatted number of the end user (your contact)
to_number	string	E.164-formatted number of the intended recipient
was_downgraded	boolean	true if iMessage was unavailable and SMS was used instead
plan	string	Arnio account plan associated with the request

Message Status Values

Status	Description
QUEUED	Message has been validated and queued for delivery
SENT	Message was sent from Arnio’s servers
DELIVERED	Delivery confirmed (iMessage only)
READ	End user has read the message (iMessage only)
FAILED	Message failed to send (see error_code and error_message for details)

Limits

Messages sent through the Arnio API must be fewer than 18,996 characters in length. For longer content, we recommend splitting it into multiple, smaller messages to ensure reliable delivery.

Useful Information

From Number

CAUTION: Arnio prioritizes deliverability and end-user experience. Each of your customers will consistently interact with your brand through one dedicated Arnio phone number, ensuring continuity and trust.

However, depending on your setup and number pooling configuration, different customers may see different Arnio numbers assigned to them. Once assigned, all future conversations with that contact will remain tied to the same number. The from_number field is included in API responses for convenience, allowing you to:

Track which number was used to send a given message.
Inform customers which number they should expect messages from.

Handle

Every message processed by Arnio includes a unique message_handle. You can use this handle to:

Query the current status of a message.
Track messages in high-volume campaigns.
Resolve situations where a message remains QUEUED or times out.

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Send Message

Supported Endpoints

Sending Files

Status Callbacks

Callback Body Fields

Message Status Values

Limits

Useful Information

From Number

Handle

​Supported Endpoints

​Sending Files

​Status Callbacks

​Callback Body Fields

​Message Status Values

​Limits

​Useful Information

​From Number

​Handle

Supported Endpoints

Sending Files

Status Callbacks

Callback Body Fields

Message Status Values

Limits

Useful Information

From Number

Handle