Send SMS & MMS via API

Connect my tools3 min readUpdated 2026-03-12

Send SMS & MMS via API

The SMS endpoint lets you send text and multimedia messages from your JustCall numbers through a simple API call. Use it for transactional alerts, appointment reminders, follow-ups, or any conversational messaging workflow.

Endpoint

POST https://api.justcall.io/v2/texts/send

Request Parameters

Parameter	Type	Required	Description
`from`	string	Yes	Your JustCall SMS-enabled number (E.164 format)
`to`	string	Yes	Recipient phone number (E.164 format)
`body`	string	Yes	Message text (up to 1,600 characters)
`media_url`	string	No	Publicly accessible URL of an image or file to send as MMS
`webhook_url`	string	No	URL to receive delivery status updates

Code Example: Send an SMS

curl -X POST "https://api.justcall.io/v2/texts/send" \
  -H "Authorization: {api_key}:{api_secret}" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "+14155551234",
    "to": "+14155559876",
    "body": "Hi Alex, your appointment is confirmed for tomorrow at 2 PM."
  }'

Code Example: Send an MMS

curl -X POST "https://api.justcall.io/v2/texts/send" \
  -H "Authorization: {api_key}:{api_secret}" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "+14155551234",
    "to": "+14155559876",
    "body": "Here is your invoice for March.",
    "media_url": "https://yourapp.com/invoices/march-2026.pdf"
  }'

Successful Response

{
  "status": "success",
  "message": "Message sent",
  "data": {
    "message_id": "msg_4d9e1a7f",
    "from": "+14155551234",
    "to": "+14155559876",
    "direction": "outbound",
    "status": "queued"
  }
}

Character Limits and Segment Billing

SMS messages are billed per segment. A single segment supports up to 160 GSM-7 characters (standard Latin letters, numbers, and common symbols). If your message uses Unicode (emojis, non-Latin scripts), the limit drops to 70 characters per segment.

Encoding	Characters per segment	Max characters (concatenated)
GSM-7	160	1,600 (10 segments)
Unicode	70	1,120 (16 segments)

Messages longer than one segment are automatically split and reassembled on the recipient's device, but each segment is billed individually.

Delivery Status Webhook

If you include a webhook_url, JustCall sends a POST request when the delivery status changes:

Status	Description
`queued`	Message accepted and queued for delivery
`sent`	Message sent to carrier
`delivered`	Carrier confirmed delivery
`failed`	Message could not be delivered
`undelivered`	Carrier rejected the message

The webhook payload includes message_id, status, to, from, and timestamp.

MMS Supported Media Types

Type	Formats	Max size
Image	JPEG, PNG, GIF	5 MB
File	PDF, VCF	5 MB
Video	MP4 (carrier support varies)	5 MB

Error Handling

Code	Meaning	Fix
400	Missing `from`, `to`, or `body`	Include all required fields
404	`from` number not found or not SMS-enabled	Use an SMS-enabled JustCall number
422	Message body exceeds character limit	Shorten the message to 1,600 characters or fewer
429	Rate limit exceeded	Retry with exponential backoff