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Send an SMS message to one or more phone numbers.

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Request Body

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to
string | string[]
required
The recipient phone number(s) in E.164 format (e.g., +14155551234). Can be a single number or an array of up to 100 numbers.
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body
string
required
The SMS message content. Maximum 1600 characters (will be split into multiple segments if needed).
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from
string
Optional alphanumeric sender ID (1-11 characters, e.g., Unosend). Note: Not all countries support custom sender IDs. If not provided, defaults to Unosend.
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metadata
object
Custom key-value pairs to attach to the message for your reference.
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tags
string[]
Tags to categorize the message for filtering and analytics.

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Response

Returns an array of results for each recipient.
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data
array

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Segment Calculation

SMS messages are charged per segment:
  • GSM-7 encoding (standard characters): 160 characters per segment
  • Unicode/UCS-2 (emojis, special chars): 70 characters per segment
  • Multi-part messages: 153 chars (GSM-7) or 67 chars (Unicode) per segment due to header overhead

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Example

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"
  }'

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Response Example

{
  "data": [
    {
      "id": "sms_abc123",
      "to": "+14155551234",
      "status": "sent",
      "message_id": "acs_xyz789",
      "segments": 1
    }
  ]
}

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Pricing

SMS is pay-as-you-go from your wallet balance:
  • First 10 SMS: Free (per organization, lifetime)
  • After free tier: $0.01 per SMS segment
Add funds to your wallet at Settings → Wallet to send SMS beyond the free tier.

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Delivery Reports

SMS delivery status is automatically updated via webhooks. You can:
  1. Check status by fetching the message: GET /v1/sms/{id}
  2. Set up webhooks to receive delivery notifications

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Opt-Out Handling

Recipients can opt out by replying STOP to any message. Unosend automatically:
  • Blocks future messages to opted-out numbers
  • Returns an error when attempting to send to opted-out recipients
  • Processes opt-in requests when recipients reply START