Sending SMS - Unosend

Overview

Unosend provides a simple API for sending SMS messages. Perfect for:

OTP & Verification

Two-factor authentication and phone verification

Transactional Alerts

Order confirmations, shipping updates, appointments

Notifications

Account alerts, reminders, status updates

Marketing

Promotional messages (with consent)

Pricing

Item	Price
First 10 SMS	Free
Additional SMS	$0.01 per segment

SMS messages are charged per segment. A segment is 160 characters for GSM-7 encoding (standard text) or 70 characters for Unicode (emojis, special characters).

Quick Start

Send Your First SMS

cURL

curl -X POST https://www.unosend.co/api/v1/sms \
  -H "Authorization: Bearer un_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "to": "+14155551234",
    "body": "Your verification code is 123456"
  }'

Response

{
  "data": {
    "id": "sms_abc123xyz",
    "to": "+14155551234",
    "body": "Your verification code is 123456",
    "status": "sent",
    "segments": 1,
    "created_at": "2026-01-15T10:30:00Z"
  }
}

SDK Examples

const response = await fetch('https://www.unosend.co/api/v1/sms', {
  method: 'POST',
  headers: {
    'Authorization': 'Bearer un_your_api_key',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    to: '+14155551234',
    body: 'Your verification code is 123456',
  }),
});

const data = await response.json();
console.log(data.data.id); // sms_abc123xyz

Phone Number Format

Always use E.164 format for phone numbers:

Country	Format	Example
USA/Canada	`+1XXXXXXXXXX`	`+14155551234`
UK	`+44XXXXXXXXXX`	`+447700900123`
Germany	`+49XXXXXXXXXXX`	`+4915123456789`
India	`+91XXXXXXXXXX`	`+919876543210`
Australia	`+61XXXXXXXXX`	`+61412345678`

Phone numbers must include the country code with + prefix. Numbers without country codes will be rejected.

Segment Calculation

SMS messages are split into segments based on character encoding:

Encoding	Single SMS	Multi-part SMS
GSM-7 (standard text)	160 chars	153 chars/segment
Unicode (emojis, etc.)	70 chars	67 chars/segment

Examples

Message	Characters	Encoding	Segments
”Your code is 123456”	19	GSM-7	1
”Hello! 👋 Welcome”	16	Unicode	1
200-char text message	200	GSM-7	2
150-char with emoji	150	Unicode	3

Use standard ASCII characters when possible to maximize message length and minimize costs.

Batch Sending

Send to multiple recipients in a single API call (max 100 per request):

cURL

curl -X POST https://www.unosend.co/api/v1/sms \
  -H "Authorization: Bearer un_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "to": ["+14155551234", "+14155555678", "+447700900123"],
    "body": "Flash sale! 50% off all items today."
  }'

Response

{
  "data": [
    { "id": "sms_abc123", "to": "+14155551234", "status": "sent", "segments": 1 },
    { "id": "sms_def456", "to": "+14155555678", "status": "sent", "segments": 1 },
    { "id": "sms_ghi789", "to": "+447700900123", "status": "sent", "segments": 1 }
  ]
}

For more details, see the Batch SMS API Reference.

OTP Verification

Unosend provides a built-in OTP verification flow:

Step 1: Send OTP

curl -X POST https://www.unosend.co/api/v1/sms/verify/send \
  -H "Authorization: Bearer un_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "to": "+14155551234"
  }'

This sends a 6-digit code to the user.

Step 2: Verify OTP

curl -X POST https://www.unosend.co/api/v1/sms/verify/check \
  -H "Authorization: Bearer un_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "to": "+14155551234",
    "code": "123456"
  }'

Response

{
  "data": {
    "verified": true,
    "phone": "+14155551234"
  }
}

Sender ID

You can customize the sender name that appears on recipients’ phones:

{
  "to": "+14155551234",
  "body": "Your order has shipped!",
  "from": "MyStore"
}

Sender ID support varies by country:

✅ Supported: UK, Germany, France, Australia, most of Europe
❌ Not supported: USA, Canada (shows a phone number instead)
⚠️ Requires registration: India (DLT), Singapore, others

Country-Specific Requirements

India (DLT Registration)

Sending SMS to India requires DLT registration:

Register with a DLT portal (JioTrueConnect, Vodafone DLT, etc.)
Register your sender ID (header)
Register message templates
Provide your DLT Entity ID and Template ID

Without DLT registration, SMS to India may be blocked by carriers. Contact support for assistance with DLT setup.

United States (10DLC)

For high-volume SMS to US numbers, register for 10DLC:

Required for sending at scale
Improves deliverability
Contact support to register your brand and campaigns

Wallet & Billing

SMS is billed from your wallet balance:

First 10 SMS are free
After that, each segment costs $0.01
Balance is deducted after successful sends
Add funds at Settings → Wallet

Check Balance Before Sending

The API returns a 402 Payment Required error if balance is insufficient:

{
  "error": "Insufficient wallet balance ($0.00). Add funds to send SMS. Estimated cost: $0.01"
}

Message Status

Track SMS delivery status:

Status	Description
`queued`	Message accepted, pending send
`sent`	Sent to carrier
`delivered`	Confirmed delivered to device
`failed`	Delivery failed
`undelivered`	Carrier could not deliver

Get SMS Status

curl https://www.unosend.co/api/v1/sms/sms_abc123 \
  -H "Authorization: Bearer un_your_api_key"

Best Practices

Use E.164 format

Always include country code with + prefix. Validate phone numbers before sending.

Keep messages concise

Shorter messages = fewer segments = lower costs. Aim for under 160 characters.

Avoid Unicode when possible

Emojis and special characters reduce segment capacity from 160 to 70 characters.

Handle opt-outs

Respect STOP requests. We automatically handle opt-outs for compliant messaging.

Include opt-out instructions

For marketing messages, include “Reply STOP to unsubscribe” as required by regulations.

Rate limit your sends

Spread large sends over time to avoid carrier throttling.

Rate Limits

Plan	SMS per minute
Free	10
Pro	100
Scale	500
Enterprise	Custom

Error Codes

Code	Meaning
400	Invalid phone number or request
401	Invalid API key
402	Insufficient wallet balance
429	Rate limit exceeded
500	Internal error

Next Steps

SMS API Reference

Full API documentation

Batch SMS

Send to multiple recipients

OTP Verification

Built-in verification flow

Webhooks

Get delivery notifications

Getting Started

Guides

Integrations

Tools

Resources

​Overview

OTP & Verification

Transactional Alerts

Notifications

Marketing

​Pricing

​Quick Start

​Send Your First SMS

​Response

​SDK Examples

​Phone Number Format

​Segment Calculation

​Examples

​Batch Sending

​Response

​OTP Verification

​Step 1: Send OTP

​Step 2: Verify OTP

​Response

​Sender ID

​Country-Specific Requirements

​India (DLT Registration)

​United States (10DLC)

​Wallet & Billing

​Check Balance Before Sending

​Message Status

​Get SMS Status

​Best Practices

​Rate Limits

​Error Codes

​Next Steps

SMS API Reference

Batch SMS

OTP Verification

Webhooks

Overview

Pricing

Quick Start

Send Your First SMS

Response

SDK Examples

Phone Number Format

Segment Calculation

Examples

Batch Sending

Response

OTP Verification

Step 1: Send OTP

Step 2: Verify OTP

Response

Sender ID

Country-Specific Requirements

India (DLT Registration)

United States (10DLC)

Wallet & Billing

Check Balance Before Sending

Message Status

Get SMS Status

Best Practices

Rate Limits

Error Codes

Next Steps