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Integrate PayPal payment processing with support for express checkout, subscriptions, and refund management...
The following are external prerequisites, not bundled files: <support-root>/references/express-checkout.md, <support-root>/references/ipn-handling.md, <support-root>/references/refund-workflows.md, <support-root>/references/billing-agreements.md, <support-root>/assets/paypal-client.py, <support-root>/assets/ipn-processor.py, <support-root>/assets/recurring-billing.py. Obtain them from the original source or an existing installation and inspect them before use. Do not execute or claim completion of a dependent step until its required file exists; report unavailable steps. The fully documented inline workflow remains usable within the authorized scope.
Master PayPal payment integration including Express Checkout, IPN handling, recurring billing, and refund workflows.
PayPal Checkout
PayPal Subscriptions
PayPal Payouts
Client-Side (JavaScript SDK)
Server-Side (REST API)
Use the current JavaScript SDK with Orders v2 endpoints on your authenticated backend. Do not combine browser-side capture with a second backend capture, and do not pass Orders v2 IDs to the legacy Payments v1 SDK.
// Browser fragment; include the SDK with the public client ID, never the client secret.
paypal.Buttons({
async createOrder() {
const response = await fetch('/api/paypal/orders', {method: 'POST'});
if (!response.ok) throw new Error('Order creation failed');
return (await response.json()).id;
},
async onApprove(data) {
const response = await fetch('/api/paypal/capture', {
method: 'POST', headers: {'Content-Type': 'application/json'},
body: JSON.stringify({orderID: data.orderID})
});
if (!response.ok) throw new Error('Capture confirmation failed');
// Backend owns reconciliation/fulfilment; the browser callback is not payment evidence.
}
}).render('#paypal-button-container');
The route handlers are application adapters, not bundled. They must authenticate the user, enforce CSRF/origin controls, bind the order to the owned cart, derive price/currency/payee from trusted data, persist a stable PayPal-Request-Id per operation, and verify capture status/amount/currency/payee before atomic fulfilment. Treat timeout as uncertain; reconcile the existing request rather than create another charge. Store secrets through the server environment/secret manager. Use Decimal/string amounts with currency-specific precision, never binary floats for money. The following fragments are sandbox examples, not a production payment system.
import requests
import json
class PayPalClient:
def __init__(self, client_id, client_secret, mode='sandbox'):
if mode not in ('sandbox', 'live'):
raise ValueError('Explicit sandbox or live mode required')
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), timeout=15, allow_redirects=False
)
response.raise_for_status()
return response.json()['access_token']
def create_order(self, amount, request_id, currency='USD'):
"""Create a PayPal order."""
url = f"{self.base_url}/v2/checkout/orders"
headers = {
"Content-Type": "application/json",
"PayPal-Request-Id": request_id, # Persisted per operation, unchanged on retry.
"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, timeout=15, allow_redirects=False)
response.raise_for_status()
return response.json()
def capture_order(self, order_id, request_id):
"""Capture payment for an order."""
url = f"{self.base_url}/v2/checkout/orders/{order_id}/capture"
headers = {
"Content-Type": "application/json",
"PayPal-Request-Id": request_id, # Persisted per operation, unchanged on retry.
"Authorization": f"Bearer {self.access_token}"
}
response = requests.post(url, headers=headers, timeout=15, allow_redirects=False)
response.raise_for_status()
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, timeout=15, allow_redirects=False)
response.raise_for_status()
return response.json()
IPN is a legacy notification protocol, not the REST Webhooks API. For current REST integrations verify webhook signatures with the documented webhook ID and environment. Limit inbound request size. VERIFIED establishes origin only: validate receiver, currency, amount, owned invoice/order and transaction status, then deduplicate atomically with a unique event/transaction record. A check-then-act helper alone races. Process reversals/refunds against original records and acknowledge only after durable recording.
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
raw_ipn = request.get_data(cache=True)
ipn_data = request.form.to_dict()
# Verify IPN with PayPal
if not verify_ipn(raw_ipn):
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(raw_ipn):
"""Echo original encoded body in order; do not reconstruct it from a dict."""
paypal_url = 'https://ipnpb.sandbox.paypal.com/cgi-bin/webscr'
response = requests.post(paypal_url, data=b'cmd=_notify-validate&' + raw_ipn,
headers={'Content-Type': 'application/x-www-form-urlencoded'},
timeout=15, allow_redirects=False)
response.raise_for_status()
return response.text.strip() == '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}")
Mutation examples require a persisted operation-specific PayPal-Request-Id where supported, immutable server-owned amounts and opaque validated resource IDs. Token expiry/refresh, verified merchant identity and durable event processing are required integration work; no fragment implements fulfilment by itself. Refunds and recurring charges require authorization for that exact operation.
def create_subscription_plan(name, amount, request_id, 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}",
"PayPal-Request-Id": request_id
}
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, timeout=15, allow_redirects=False)
response.raise_for_status()
return response.json()
def create_subscription(plan_id, subscriber_email, request_id):
"""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}",
"PayPal-Request-Id": request_id
}
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, timeout=15, allow_redirects=False)
response.raise_for_status()
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']
}
def create_refund(capture_id, request_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",
"PayPal-Request-Id": request_id,
"Authorization": f"Bearer {client.access_token}"
}
payload = {}
if amount is not None:
payload["amount"] = {
"value": str(amount),
"currency_code": "USD"
}
# Validate positive Decimal refund <= remaining captured balance and capture currency first.
if note:
payload["note_to_payer"] = note
response = requests.post(url, headers=headers, json=payload, timeout=15, allow_redirects=False)
response.raise_for_status()
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, timeout=15, allow_redirects=False)
response.raise_for_status()
return response.json()
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", persisted_request_id))
except PayPalError as e:
# Handle error appropriately
log_error(e)
# Use sandbox credentials
import os
SANDBOX_CLIENT_ID = os.environ["PAYPAL_SANDBOX_CLIENT_ID"]
SANDBOX_SECRET = os.environ["PAYPAL_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", "sandbox-test-order-001")
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'], 'sandbox-test-capture-001')
# assert captured['status'] == 'COMPLETED'
