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Overview

VoicePact uses Africa’s Talking as its primary telecommunications provider for voice calls, SMS messaging, USSD sessions, and mobile money payments. The integration provides a robust, circuit-breaker-protected client with retry logic and comprehensive error handling.

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Architecture

The Africa’s Talking client is implemented in app/services/africastalking_client.py and provides:
  • Voice Services: Automated voice calls and conference recording
  • SMS Services: Bulk SMS with delivery tracking
  • USSD Services: Interactive menu-based contract management
  • Payment Services: Mobile money checkout and escrow management
  • Circuit Breaker: Automatic failover protection
  • Webhook Verification: HMAC-based signature validation

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Configuration

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Environment Variables

Configure the following environment variables in your .env file: 
# Africa's Talking Credentials
AT_USERNAME=sandbox                    # Your AT username (use 'sandbox' for testing)
AT_API_KEY=your_api_key_here          # Your AT API key

# Voice Configuration
AT_VOICE_NUMBER=+254XXXXXXXXX         # Your AT voice number

# USSD Configuration
AT_USSD_SERVICE_CODE=*483#            # Your USSD service code

# Payment Configuration
AT_PAYMENT_PRODUCT_NAME=VoicePact     # Product name for payments

# Webhook Security
WEBHOOK_SECRET=your_webhook_secret    # Secret for webhook signature validation
WEBHOOK_BASE_URL=https://your-domain.com  # Base URL for webhooks

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Configuration Class

The settings are managed by the Settings class in app/core/config.py:80-104: 
class Settings(BaseSettings):
    # Africa's Talking API Configuration
    at_username: str = Field(default="sandbox")
    at_api_key: SecretStr = Field(...)
    at_voice_number: str = Field(default="+254XXXXXXXXX")
    at_payment_product_name: str = Field(default="VoicePact")
    at_ussd_service_code: str = Field(default="*483#")

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Client Initialization

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Basic Setup

The client is initialized as a singleton instance: 
from app.services.africastalking_client import get_africastalking_client

# In your FastAPI endpoint
at_client = await get_africastalking_client()

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Client Architecture

The AfricasTalkingClient class (lines 68-113) includes: 
class AfricasTalkingClient:
    def __init__(self):
        self.username = settings.at_username
        self.api_key = settings.get_secret_value('at_api_key')
        self.voice_number = settings.at_voice_number
        self.service_code = settings.at_ussd_service_code
        
        africastalking.initialize(self.username, self.api_key)
        
        # Initialize services
        self.sms_service = africastalking.SMS
        self.voice_service = africastalking.Voice
        self.payment_service = africastalking.Payment
        
        # Circuit breakers for fault tolerance
        self.sms_circuit_breaker = CircuitBreaker()
        self.voice_circuit_breaker = CircuitBreaker()
        self.payment_circuit_breaker = CircuitBreaker()

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Voice Services

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Making Voice Calls

Initiate voice calls with automatic retry logic: 
# Make a voice call (app/services/africastalking_client.py:201-221)
response = await at_client.make_voice_call(
    recipients=["+254712345678", "+254723456789"],
    from_number=None  # Uses configured voice number
)
Response Format: 
{
  "sessionId": "ATVId_abc123...",
  "status": "Success",
  "entries": [
    {
      "phoneNumber": "+254712345678",
      "status": "Queued"
    }
  ]
}

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Voice Webhooks

Voice webhooks are handled at /api/v1/voice/webhook (see app/api/v1/endpoints/voice.py:223-258): Webhook Payload: 
# Received from Africa's Talking
{
    "sessionId": "ATVId_...",
    "phoneNumber": "+254712345678",
    "recordingUrl": "https://voice.africastalking.com/recordings/...",
    "duration": 120,  # seconds
    "status": "completed"
}
Handler Implementation: 
@router.post("/webhook")
async def voice_webhook(
    request: Request,
    at_client: AfricasTalkingClient = Depends(get_africastalking_client),
    db: AsyncSession = Depends(get_db)
):
    form_data = await request.form()
    
    session_id = form_data.get("sessionId")
    recording_url = form_data.get("recordingUrl")
    duration = form_data.get("duration")
    
    # Update recording in database
    recording = await db.get(VoiceRecording, session_id)
    if recording:
        recording.recording_url = recording_url
        recording.duration = int(duration) if duration else None
        await db.commit()
    
    return {"status": "webhook_processed"}

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SMS Services

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Sending SMS

Send SMS with automatic retry and circuit breaker protection: 
# Send single SMS (app/services/africastalking_client.py:136-161)
response = await at_client.send_sms(
    message="Your VoicePact contract is ready for review.",
    recipients=["+254712345678"],
    sender_id="VoicePact",  # Optional
    enqueue=False
)
Response Format: 
{
  "SMSMessageData": {
    "Message": "Sent to 1/1 Total Cost: KES 0.8000",
    "Recipients": [
      {
        "statusCode": 101,
        "number": "+254712345678",
        "status": "Success",
        "cost": "KES 0.8000",
        "messageId": "ATXid_..."
      }
    ]
  }
}

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Bulk SMS

Send messages to multiple recipients: 
# Send bulk SMS (app/services/africastalking_client.py:167-182)
messages = [
    {
        "message": "Contract AG-001 ready for signing",
        "recipients": ["+254712345678"]
    },
    {
        "message": "Payment received for contract AG-001",
        "recipients": ["+254723456789"]
    }
]

responses = await at_client.send_bulk_sms(
    messages=messages,
    sender_id="VoicePact"
)

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SMS Templates

The client provides built-in SMS templates:

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Contract Notification

# Generate contract SMS (app/services/africastalking_client.py:407-430)
message = at_client.generate_contract_sms(
    contract_id="AG-2024-001",
    contract_terms={
        "product": "Maize",
        "quantity": 100,
        "unit": "bags",
        "total_amount": 50000,
        "currency": "KES",
        "delivery_deadline": "2024-04-15"
    }
)

# Output:
# VoicePact Contract Summary:
# ID: AG-2024-001
# Product: Maize (100 bags)
# Total: KES 50,000.00, Due: 2024-04-15
# Reply YES-AG-2024-001 to confirm or NO-AG-2024-001 to decline

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Payment Notification

# Generate payment SMS (app/services/africastalking_client.py:433-446)
message = at_client.generate_payment_sms(
    contract_id="AG-2024-001",
    amount=50000,
    currency="KES",
    action="received"
)

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SMS Webhooks

Handle incoming SMS and delivery reports at /api/v1/sms/webhook (see app/api/v1/endpoints/sms.py:293-328): Webhook Payload: 
# Incoming SMS
{
    "from": "+254712345678",
    "to": "40404",
    "text": "YES-AG-2024-001",
    "date": "2024-03-06 10:30:00",
    "id": "ATXid_...",
    "linkId": "SampleLinkId123"
}

# Delivery report
{
    "id": "ATXid_...",
    "status": "Success",
    "phoneNumber": "+254712345678",
    "retryCount": 0
}
Handler Example: 
@router.post("/webhook")
async def sms_webhook(request: Request):
    form_data = await request.form()
    
    phone_number = form_data.get("from")
    message = form_data.get("text", "").upper().strip()
    
    # Handle contract confirmation
    if message.startswith("YES-") or message.startswith("NO-"):
        contract_id = message.split("-", 1)[1]
        action = "confirm" if message.startswith("YES-") else "reject"
        
        logger.info(f"Contract {action}: {contract_id} from {phone_number}")
        
        return {
            "action": action,
            "contract_id": contract_id,
            "phone_number": phone_number
        }
    
    return {"status": "webhook_received"}

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USSD Services

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USSD Menu Flow

USSD menus are handled at /api/v1/ussd/ (see app/api/v1/endpoints/ussd.py): Main Menu: 
def main_menu() -> str:
    return """Welcome to VoicePact
1. View My Contracts
2. Confirm Delivery
3. Check Payments
4. Help & Support
0. Exit"""

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Building USSD Responses

Use the utility methods to build USSD responses: 
# Continue session (app/services/africastalking_client.py:382-385)
response = at_client.build_ussd_response(
    text="Select an option:",
    end_session=False  # CON response
)

# End session
response = at_client.build_ussd_response(
    text="Thank you for using VoicePact!",
    end_session=True  # END response
)

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USSD Request Format

Webhook Payload: 
{
    "sessionId": "ATUid_...",
    "serviceCode": "*483#",
    "phoneNumber": "+254712345678",
    "text": "1*2*3"  # User navigation path
}

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USSD Handler Implementation

@router.post("/")
async def ussd_handler(
    request: Request,
    sessionId: str = Form(...),
    serviceCode: str = Form(...),
    phoneNumber: str = Form(...),
    text: str = Form(""),
    at_client: AfricasTalkingClient = Depends(get_africastalking_client),
    db: AsyncSession = Depends(get_db)
):
    # Parse user input
    user_input = text.split('*')[-1] if text else ""
    
    # First request - show main menu
    if not text:
        return at_client.build_ussd_response(main_menu(), end_session=False)
    
    # Handle menu navigation
    if user_input == "1":
        # Get user contracts
        contracts = await get_user_contracts(phoneNumber, db)
        menu_text = "Your Contracts:\n"
        for i, contract in enumerate(contracts[:5], 1):
            menu_text += f"{i}. {contract.id[:12]}...\n"
        return at_client.build_ussd_response(menu_text, end_session=False)
    
    # Exit
    elif user_input == "0":
        return at_client.build_ussd_response(
            "Thank you!", end_session=True
        )

​
Payment Services

See Mobile Money Integration for detailed payment documentation.

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Mobile Checkout

# Initiate checkout (app/services/africastalking_client.py:240-268)
response = await at_client.mobile_checkout(
    phone_number="+254712345678",
    amount=50000,
    currency_code="KES",
    metadata={
        "contract_id": "AG-2024-001",
        "payment_type": "escrow"
    }
)

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Circuit Breaker

The client implements circuit breaker pattern for fault tolerance:

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Circuit Breaker States

class CircuitBreaker:
    def __init__(
        self,
        failure_threshold: int = 5,      # Failures before opening
        recovery_timeout: int = 60,      # Seconds before retry
        expected_exception=Exception
    ):
        self.state = 'CLOSED'  # CLOSED, OPEN, HALF_OPEN
States:
  • CLOSED: Normal operation, requests pass through
  • OPEN: Too many failures, requests blocked
  • HALF_OPEN: Testing if service recovered

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Usage Example

# Circuit breaker automatically protects service calls
try:
    response = await at_client.send_sms(
        message="Test message",
        recipients=["+254712345678"]
    )
except CircuitBreakerOpen:
    logger.error("SMS service unavailable - circuit breaker open")
    # Handle gracefully

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Webhook Security

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Signature Verification

Verify webhook authenticity using HMAC signatures: 
# Verify webhook (app/services/africastalking_client.py:119-129)
@router.post("/webhook")
async def secure_webhook(request: Request):
    body = await request.body()
    signature = request.headers.get("X-Africastalking-Signature")
    
    # Verify signature
    if not at_client.verify_webhook_signature(
        payload=body.decode(),
        signature=signature
    ):
        raise HTTPException(status_code=401, detail="Invalid signature")
    
    # Process webhook
    ...

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Implementation

def verify_webhook_signature(self, payload: str, signature: str) -> bool:
    if not self.webhook_secret or not signature:
        return False
    
    expected_signature = hmac.new(
        self.webhook_secret.encode(),
        payload.encode(),
        hashlib.sha256
    ).hexdigest()
    
    return hmac.compare_digest(f"sha256={expected_signature}", signature)

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Error Handling

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Custom Exceptions

class AfricasTalkingException(Exception):
    def __init__(
        self,
        message: str,
        error_code: Optional[str] = None,
        response_data: Optional[dict] = None
    ):
        self.message = message
        self.error_code = error_code
        self.response_data = response_data or {}

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Retry Logic

Automatic retry with exponential backoff: 
from tenacity import retry, stop_after_attempt, wait_exponential

@retry(
    stop=stop_after_attempt(3),
    wait=wait_exponential(multiplier=1, min=1, max=10),
    retry=retry_if_exception_type((httpx.TimeoutException, httpx.ConnectError))
)
async def send_sms(...):
    # Automatically retries on timeout/connection errors
    ...

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Health Checks

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Service Status

# Check service health (app/services/africastalking_client.py:520-543)
health = await at_client.health_check()

# Returns:
{
    "sms_service": "healthy",
    "payment_service": "healthy",
    "voice_service": "healthy",
    "sms_circuit": "CLOSED",
    "voice_circuit": "CLOSED",
    "payment_circuit": "CLOSED"
}

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Testing

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Sandbox Mode

Use Africa’s Talking sandbox for testing: 
# .env for development
AT_USERNAME=sandbox
AT_API_KEY=your_sandbox_api_key

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Test Endpoints

# Test SMS
curl -X POST "http://localhost:8000/api/v1/sms/test?phone_number=+254712345678"

# Test Voice
curl -X POST "http://localhost:8000/api/v1/voice/conference/create" \
  -H "Content-Type: application/json" \
  -d '{"parties": ["+254712345678", "+254723456789"]}'

# Test Payment
curl -X POST "http://localhost:8000/api/v1/payments/test/checkout?phone_number=+254712345678&amount=100"

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Best Practices

  1. Use Circuit Breakers: Let the built-in circuit breakers protect your services
  2. Verify Webhooks: Always verify webhook signatures in production
  3. Format Phone Numbers: Use format_phone_number() for consistent formatting
  4. Handle Retries: Configure appropriate retry limits for your use case
  5. Monitor Health: Regularly check service health status
  6. Log Everything: Comprehensive logging helps debug integration issues
  7. Test in Sandbox: Always test with sandbox credentials first

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Troubleshooting

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Common Issues

SMS Not Sending: 
# Check API key
if not at_client.sms_service:
    logger.error("SMS service not initialized - check AT_API_KEY")

# Check phone number format
formatted = await at_client.format_phone_number("+254712345678")
valid = await at_client.validate_phone_number(formatted)
Circuit Breaker Open: 
# Wait for recovery or manually reset
at_client.sms_circuit_breaker.reset()
Webhook Not Receiving:
  • Verify webhook URL is publicly accessible
  • Check firewall settings
  • Validate webhook signature configuration
  • Review Africa’s Talking dashboard logs

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Next Steps

Mobile Money

Learn about mobile money integration

Webhooks

Complete webhook configuration guide

API Reference

Full API documentation

Voice Processing

Voice recording and processing

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