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Overview

The IXO USSD gateway exposes a single session endpoint that telecom gateways call for each user interaction, plus debug and health endpoints for operators. All endpoints accept and return JSON unless otherwise noted. The main session endpoint returns plain text in the USSD response format.

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Authentication

The /api/ussd endpoint does not require authentication by default. It is intended to be called by your telecom gateway server, not directly from a browser. Restrict access at the network or reverse-proxy layer in production.

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Base URL

http://YOUR_SERVER:3000
The default port is 3000. Set PORT in your environment to override.

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Session endpoint

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POST /api/ussd

Processes a USSD interaction. Called by the telecom gateway once per user input during a session. Request 
{
  "sessionId": "string",
  "serviceCode": "string",
  "phoneNumber": "string",
  "text": "string"
}
  • Type: string
  • Required: yes
  • Description: Unique session identifier assigned by the telecom gateway.
  • Type: string
  • Required: yes
  • Description: USSD service code the user dialled, for example *1234#.
  • Type: string
  • Required: yes
  • Description: User phone number in E.164 international format, for example +260971234567.
  • Type: string
  • Required: yes
  • Description: User input accumulated during the session; empty string on initial dial.
Validation rules
  • phoneNumber must be E.164 format
  • serviceCode must match USSD format, e.g. *1234# or *123*456#
  • text maximum 182 characters (USSD protocol limit)
  • sessionId maximum 100 characters
Response Plain text. The first word indicates whether the session continues or ends. 
CON <menu text>

END <closing message>
  • Meaning: Session continues; display the menu and wait for the next input.
  • Meaning: Session closed; display the message and end the USSD session.
Example — initial dial 
curl -X POST http://localhost:3000/api/ussd \
  -H "Content-Type: application/json" \
  -d '{
    "sessionId": "session-001",
    "serviceCode": "*1234#",
    "phoneNumber": "+260971234567",
    "text": ""
  }'
Response: 
CON Welcome to IXO USSD
1. Know More
2. Account Menu
*. Exit
Example — user selects option 1 
curl -X POST http://localhost:3000/api/ussd \
  -H "Content-Type: application/json" \
  -d '{
    "sessionId": "session-001",
    "serviceCode": "*1234#",
    "phoneNumber": "+260971234567",
    "text": "1"
  }'
Response: 
CON Information Center
1. About this service
2. Pricing
3. Delivery
*. Exit

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Debug endpoints

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GET /api/ussd/debug/:sessionId

Returns the current state and context for an active session. Intended for operator debugging only — do not expose publicly. Response 
{
  "sessionId": "session-001",
  "debugInfo": {
    "state": "preMenu",
    "context": {
      "sessionId": "session-001",
      "phoneNumber": "+260971234567",
      "message": "Welcome to IXO USSD...",
      "isAuthenticated": false
    },
    "status": "active"
  },
  "activeSessions": ["session-001"]
}

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GET /api/ussd/sessions

Returns all currently active session IDs. 
{
  "activeSessions": ["session-001", "session-002"],
  "count": 2
}

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Health endpoints

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GET /health

Returns application health with database connectivity status. 
{
  "status": "ok",
  "environment": "production",
  "timestamp": "2026-04-22T10:00:00.000Z",
  "uptime": 3600,
  "database": "connected"
}

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GET /

Basic health check for platform-as-a-service health probes. 
{
  "status": "ok",
  "message": "ixo-ussd-server running",
  "environment": "production",
  "timestamp": "2026-04-22T10:00:00.000Z"
}

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Errors

  • Cause: Request failed validation.
  • What to do: Check phone number is E.164, service code format, and text length.
  • Cause: Server or database error.
  • What to do: Check /health for database connectivity.
  • Cause: Session expired or never started.
  • What to do: Sessions expire after inactivity; the user must dial again.
Rate limiting: 100 requests per minute per IP address. Requests exceeding this return HTTP 429. For generic HTTP status handling (retries, 5xx, client errors), see Error handling. For environment-specific service URLs and auth, see Networks and endpoints and Authentication matrix.

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Security notes

  • User PINs are encrypted at rest with AES-256 using the PIN_ENCRYPTION_KEY environment variable.
  • All inputs are validated and sanitised before processing.
  • Set TRUST_PROXY_ENABLED=true when running behind a reverse proxy so rate limiting uses the real client IP.

Deploy the IXO USSD gateway

Set up environment configuration and telecom gateway integration.

IXO USSD gateway overview

Review architecture and the integration model.