paypal-integration skill

---
name: paypal-integration
description: PayPal payment integration for Express Checkout, subscriptions, and IPN webhooks. Use when adding PayPal as payment option, implementing PayPal recurring billing, or handling PayPal refunds and disputes. Covers Smart Payment Buttons, order capture, and subscription plan management.
---

# PayPal Integration

Master PayPal payment integration including Express Checkout, IPN handling, recurring billing, and refund workflows.

## When to Use This Skill

- Integrating PayPal as a payment option
- Implementing express checkout flows
- Setting up recurring billing with PayPal
- Processing refunds and payment disputes
- Handling PayPal webhooks (IPN)
- Supporting international payments
- Implementing PayPal subscriptions

## Core Concepts

### 1. Payment Products
**PayPal Checkout**
- One-time payments
- Express checkout experience
- Guest and PayPal account payments

**PayPal Subscriptions**
- Recurring billing
- Subscription plans
- Automatic renewals

**PayPal Payouts**
- Send money to multiple recipients
- Marketplace and platform payments

### 2. Integration Methods
**Client-Side (JavaScript SDK)**
- Smart Payment Buttons
- Hosted payment flow
- Minimal backend code

**Server-Side (REST API)**
- Full control over payment flow
- Custom checkout UI
- Advanced features

### 3. IPN (Instant Payment Notification)
- Webhook-like payment notifications
- Asynchronous payment updates
- Verification required

## Quick Start

```javascript
// Frontend - PayPal Smart Buttons
<div id="paypal-button-container"></div>

<script src="https://www.paypal.com/sdk/js?client-id=YOUR_CLIENT_ID&currency=USD"></script>
<script>
  paypal.Buttons({
    createOrder: function(data, actions) {
      return actions.order.create({
        purchase_units: [{
          amount: {
            value: '25.00'
          }
        }]
      });
    },
    onApprove: function(data, actions) {
      return actions.order.capture().then(function(details) {
        // Payment successful
        console.log('Transaction completed by ' + details.payer.name.given_name);

        // Send to backend for verification
        fetch('/api/paypal/capture', {
          method: 'POST',
          headers: {'Content-Type': 'application/json'},
          body: JSON.stringify({orderID: data.orderID})
        });
      });
    }
  }).render('#paypal-button-container');
</script>
```

```python
# Backend - Verify and capture order
from paypalrestsdk import Payment
import paypalrestsdk

paypalrestsdk.configure({
    "mode": "sandbox",  # or "live"
    "client_id": "YOUR_CLIENT_ID",
    "client_secret": "YOUR_CLIENT_SECRET"
})

def capture_paypal_order(order_id):
    """Capture a PayPal order."""
    payment = Payment.find(order_id)

    if payment.execute({"payer_id": payment.payer.payer_info.payer_id}):
        # Payment successful
        return {
            'status': 'success',
            'transaction_id': payment.id,
            'amount': payment.transactions[0].amount.total
        }
    else:
        # Payment failed
        return {
            'status': 'failed',
            'error': payment.error
        }
```

## Express Checkout Implementation

### Server-Side Order Creation
```python
import requests
import json

class PayPalClient:
    def __init__(self, client_id, client_secret, mode='sandbox'):
        self.client_id = client_id
        self.client_secret = client_secret
        self.base_url = 'https://api-m.sandbox.paypal.com' if mode == 'sandbox' else 'https://api-m.paypal.com'
        self.access_token = self.get_access_token()

    def get_access_token(self):
        """Get OAuth access token."""
        url = f"{self.base_url}/v1/oauth2/token"
        headers = {"Accept": "application/json", "Accept-Language": "en_US"}

        response = requests.post(
            url,
            headers=headers,
            data={"grant_type": "client_credentials"},
            auth=(self.client_id, self.client_secret)
        )

        return response.json()['access_token']

    def create_order(self, amount, currency='USD'):
        """Create a PayPal order."""
        url = f"{self.base_url}/v2/checkout/orders"
        headers = {
            "Content-Type": "application/json",
            "Authorization": f"Bearer {self.access_token}"
        }

        payload = {
            "intent": "CAPTURE",
            "purchase_units": [{
                "amount": {
                    "currency_code": currency,
                    "value": str(amount)
                }
            }]
        }

        response = requests.post(url, headers=headers, json=payload)
        return response.json()

    def capture_order(self, order_id):
        """Capture payment for an order."""
        url = f"{self.base_url}/v2/checkout/orders/{order_id}/capture"
        headers = {
            "Content-Type": "application/json",
            "Authorization": f"Bearer {self.access_token}"
        }

        response = requests.post(url, headers=headers)
        return response.json()

    def get_order_details(self, order_id):
        """Get order details."""
        url = f"{self.base_url}/v2/checkout/orders/{order_id}"
        headers = {
            "Authorization": f"Bearer {self.access_token}"
        }

        response = requests.get(url, headers=headers)
        return response.json()
```

## IPN (Instant Payment Notification) Handling

### IPN Verification and Processing
```python
from flask import Flask, request
import requests
from urllib.parse import parse_qs

app = Flask(__name__)

@app.route('/ipn', methods=['POST'])
def handle_ipn():
    """Handle PayPal IPN notifications."""
    # Get IPN message
    ipn_data = request.form.to_dict()

    # Verify IPN with PayPal
    if not verify_ipn(ipn_data):
        return 'IPN verification failed', 400

    # Process IPN based on transaction type
    payment_status = ipn_data.get('payment_status')
    txn_type = ipn_data.get('txn_type')

    if payment_status == 'Completed':
        handle_payment_completed(ipn_data)
    elif payment_status == 'Refunded':
        handle_refund(ipn_data)
    elif payment_status == 'Reversed':
        handle_chargeback(ipn_data)

    return 'IPN processed', 200

def verify_ipn(ipn_data):
    """Verify IPN message authenticity."""
    # Add 'cmd' parameter
    verify_data = ipn_data.copy()
    verify_data['cmd'] = '_notify-validate'

    # Send back to PayPal for verification
    paypal_url = 'https://ipnpb.sandbox.paypal.com/cgi-bin/webscr'  # or production URL

    response = requests.post(paypal_url, data=verify_data)

    return response.text == 'VERIFIED'

def handle_payment_completed(ipn_data):
    """Process completed payment."""
    txn_id = ipn_data.get('txn_id')
    payer_email = ipn_data.get('payer_email')
    mc_gross = ipn_data.get('mc_gross')
    item_name = ipn_data.get('item_name')

    # Check if already processed (prevent duplicates)
    if is_transaction_processed(txn_id):
        return

    # Update database
    # Send confirmation email
    # Fulfill order
    print(f"Payment completed: {txn_id}, Amount: ${mc_gross}")

def handle_refund(ipn_data):
    """Handle refund."""
    parent_txn_id = ipn_data.get('parent_txn_id')
    mc_gross = ipn_data.get('mc_gross')

    # Process refund in your system
    print(f"Refund processed: {parent_txn_id}, Amount: ${mc_gross}")

def handle_chargeback(ipn_data):
    """Handle payment reversal/chargeback."""
    txn_id = ipn_data.get('txn_id')
    reason_code = ipn_data.get('reason_code')

    # Handle chargeback
    print(f"Chargeback: {txn_id}, Reason: {reason_code}")
```

## Subscription/Recurring Billing

### Create Subscription Plan
```python
def create_subscription_plan(name, amount, interval='MONTH'):
    """Create a subscription plan."""
    client = PayPalClient(CLIENT_ID, CLIENT_SECRET)

    url = f"{client.base_url}/v1/billing/plans"
    headers = {
        "Content-Type": "application/json",
        "Authorization": f"Bearer {client.access_token}"
    }

    payload = {
        "product_id": "PRODUCT_ID",  # Create product first
        "name": name,
        "billing_cycles": [{
            "frequency": {
                "interval_unit": interval,
                "interval_count": 1
            },
            "tenure_type": "REGULAR",
            "sequence": 1,
            "total_cycles": 0,  # Infinite
            "pricing_scheme": {
                "fixed_price": {
                    "value": str(amount),
                    "currency_code": "USD"
                }
            }
        }],
        "payment_preferences": {
            "auto_bill_outstanding": True,
            "setup_fee": {
                "value": "0",
                "currency_code": "USD"
            },
            "setup_fee_failure_action": "CONTINUE",
            "payment_failure_threshold": 3
        }
    }

    response = requests.post(url, headers=headers, json=payload)
    return response.json()

def create_subscription(plan_id, subscriber_email):
    """Create a subscription for a customer."""
    client = PayPalClient(CLIENT_ID, CLIENT_SECRET)

    url = f"{client.base_url}/v1/billing/subscriptions"
    headers = {
        "Content-Type": "application/json",
        "Authorization": f"Bearer {client.access_token}"
    }

    payload = {
        "plan_id": plan_id,
        "subscriber": {
            "email_address": subscriber_email
        },
        "application_context": {
            "return_url": "https://yourdomain.com/subscription/success",
            "cancel_url": "https://yourdomain.com/subscription/cancel"
        }
    }

    response = requests.post(url, headers=headers, json=payload)
    subscription = response.json()

    # Get approval URL
    for link in subscription.get('links', []):
        if link['rel'] == 'approve':
            return {
                'subscription_id': subscription['id'],
                'approval_url': link['href']
            }
```

## Refund Workflows

```python
def create_refund(capture_id, amount=None, note=None):
    """Create a refund for a captured payment."""
    client = PayPalClient(CLIENT_ID, CLIENT_SECRET)

    url = f"{client.base_url}/v2/payments/captures/{capture_id}/refund"
    headers = {
        "Content-Type": "application/json",
        "Authorization": f"Bearer {client.access_token}"
    }

    payload = {}
    if amount:
        payload["amount"] = {
            "value": str(amount),
            "currency_code": "USD"
        }

    if note:
        payload["note_to_payer"] = note

    response = requests.post(url, headers=headers, json=payload)
    return response.json()

def get_refund_details(refund_id):
    """Get refund details."""
    client = PayPalClient(CLIENT_ID, CLIENT_SECRET)

    url = f"{client.base_url}/v2/payments/refunds/{refund_id}"
    headers = {
        "Authorization": f"Bearer {client.access_token}"
    }

    response = requests.get(url, headers=headers)
    return response.json()
```

## Error Handling

```python
class PayPalError(Exception):
    """Custom PayPal error."""
    pass

def handle_paypal_api_call(api_function):
    """Wrapper for PayPal API calls with error handling."""
    try:
        result = api_function()
        return result
    except requests.exceptions.RequestException as e:
        # Network error
        raise PayPalError(f"Network error: {str(e)}")
    except Exception as e:
        # Other errors
        raise PayPalError(f"PayPal API error: {str(e)}")

# Usage
try:
    order = handle_paypal_api_call(lambda: client.create_order(25.00))
except PayPalError as e:
    # Handle error appropriately
    log_error(e)
```

## Testing

```python
# Use sandbox credentials
SANDBOX_CLIENT_ID = "..."
SANDBOX_SECRET = "..."

# Test accounts
# Create test buyer and seller accounts at developer.paypal.com

def test_payment_flow():
    """Test complete payment flow."""
    client = PayPalClient(SANDBOX_CLIENT_ID, SANDBOX_SECRET, mode='sandbox')

    # Create order
    order = client.create_order(10.00)
    assert 'id' in order

    # Get approval URL
    approval_url = next((link['href'] for link in order['links'] if link['rel'] == 'approve'), None)
    assert approval_url is not None

    # After approval (manual step with test account)
    # Capture order
    # captured = client.capture_order(order['id'])
    # assert captured['status'] == 'COMPLETED'
```

## Best Practices

1. **Always Verify IPN**: Never trust IPN without verification
2. **Idempotent Processing**: Handle duplicate IPN notifications
3. **Error Handling**: Implement robust error handling
4. **Logging**: Log all transactions and errors
5. **Test Thoroughly**: Use sandbox extensively
6. **Webhook Backup**: Don't rely solely on client-side callbacks
7. **Currency Handling**: Always specify currency explicitly

## Common Pitfalls

- **Not Verifying IPN**: Accepting IPN without verification
- **Duplicate Processing**: Not checking for duplicate transactions
- **Wrong Environment**: Mixing sandbox and production URLs/credentials
- **Missing Webhooks**: Not handling all payment states
- **Hardcoded Values**: Not making configurable for different environments