Embedded Checkout Integration

Embed Gale’s secure checkout directly on your website using an iframe. Customers stay on your domain while Gale handles payment processing, eligibility verification, and compliance.

When to Use Embedded Checkout

Perfect for you if:

You want customers to stay on your website during checkout
You need a branded checkout experience
You’re building a platform or multi-tenant solution
You want Gale to handle checkout UI and compliance
You can integrate via API to create checkout sessions

How It Works

Customer adds items to cart on your website
Your site creates a checkout session via POST /v2/checkout
Gale API returns a checkout_url
Your site embeds the checkout URL in an iframe
Customer completes payment in the iframe (stays on your domain)
Gale processes the payment securely
Gale sends webhook notification with order.created event
Your site shows confirmation to customer

Implementation Steps

Create Checkout Session via API

When customer is ready to checkout, create a checkout session with their items

Embed the Checkout Iframe

Use the returned checkout_url in an iframe on your checkout page

Handle Payment Confirmation

Listen for webhooks or postMessage events to confirm payment

Fulfill the Order

Process the order and show confirmation to customer

Step 1: Create Checkout Session

Create a checkout session with customer info and line items:

POST /v2/checkout

{
  "customer": {
    "email": "customer@example.com",
    "first_name": "Jane",
    "last_name": "Doe",
    "phone": "+1-555-123-4567"
  },
  "line_items": [
    {
      "merchant_product_id": "PROD-001",
      "name": "Digital Thermometer",
      "quantity": 1,
      "price_cents": 2995
    }
  ],
  "shipping_info": {
    "address_line_1": "123 Main St",
    "city": "New York",
    "state": "NY",
    "zip": "10001",
    "country": "US"
  },
  "amounts": {
    "shipping_cents": 995,
    "tax_cents": 245
  },
  "success_url": "https://yoursite.com/checkout/success",
  "cancel_url": "https://yoursite.com/checkout/cancel",
  "metadata": {
    "internal_order_id": "your-cart-123"
  }
}

Response:

{
  "id": "checkout_abc123xyz",
  "checkout_url": "https://checkout.withgale.com/c/checkout_abc123xyz",
  "status": "open",
  "expires_at": "2025-10-19T14:30:00Z",
  "created_at": "2025-10-18T14:30:00Z"
}

Step 2: Embed Checkout

Use the checkout_url in an iframe on your page:

HTML
React
Next.js

<!DOCTYPE html>
<html>
<head>
  <title>Checkout - Your Store</title>
  <style>
    #gale-checkout {
      width: 100%;
      height: 600px;
      border: none;
      border-radius: 8px;
    }

    .checkout-container {
      max-width: 800px;
      margin: 0 auto;
      padding: 20px;
    }
  </style>
</head>
<body>
  <div class="checkout-container">
    <h1>Complete Your Purchase</h1>
    <iframe
      id="gale-checkout"
      src="https://checkout.withgale.com/c/checkout_abc123xyz"
      allow="payment">
    </iframe>
  </div>

  <script>
    // Listen for checkout completion
    window.addEventListener('message', (event) => {
      if (event.origin !== 'https://checkout.withgale.com') return;

      if (event.data.type === 'checkout.completed') {
        // Redirect to success page
        window.location.href = '/checkout/success?order_id=' + event.data.order_id;
      }

      if (event.data.type === 'checkout.cancelled') {
        // Handle cancellation
        window.location.href = '/checkout/cancel';
      }
    });
  </script>
</body>
</html>

Step 3: Handle Payment Confirmation

Option A: Webhooks (Recommended)

// /api/webhooks/gale
app.post('/webhooks/gale', async (req, res) => {
  const event = req.body;

  // Verify webhook signature
  const isValid = verifyGaleSignature(
    req.headers['x-gale-signature'],
    req.body
  );

  if (!isValid) {
    return res.status(401).send('Invalid signature');
  }

  switch (event.type) {
    case 'order.created':
      // Order was created successfully
      const { id, customer, line_items } = event.data;

      await fulfillOrder(id, line_items);
      await sendConfirmationEmail(customer.email);
      break;

    case 'checkout.failed':
      // Payment failed
      await handlePaymentFailure(event.data.checkout_id);
      break;
  }

  res.status(200).send('OK');
});

Learn more about Webhooks →

Option B: PostMessage Events

Listen for iframe postMessage events:

window.addEventListener('message', (event) => {
  if (event.origin !== 'https://checkout.withgale.com') return;

  switch (event.data.type) {
    case 'checkout.completed':
      // Payment successful
      console.log('Checkout ID:', event.data.checkout_id);
      console.log('Order ID:', event.data.order_id);

      // Show success message or redirect
      window.location.href = '/success';
      break;

    case 'checkout.cancelled':
      // Customer cancelled
      window.location.href = '/checkout';
      break;

    case 'checkout.error':
      // Error occurred
      console.error('Checkout error:', event.data.error);
      break;
  }
});

Option C: Polling (Not Recommended)

Check order status via webhooks instead of polling. If you must poll, use the Order API:

const checkOrderStatus = async (orderId) => {
  const response = await fetch(
    `https://api.withgale.com/v2/orders/${orderId}`,
    {
      headers: {
        'Authorization': `Bearer ${API_KEY}`
      }
    }
  );

  const order = await response.json();

  if (order.status === 'completed') {
    // Payment completed
    return true;
  }

  return false;
};

Subscription Support

Embedded checkout fully supports subscriptions:

{
  "line_items": [
    {
      "merchant_product_id": "MONTHLY_VITAMINS",
      "name": "Monthly Vitamin Subscription",
      "quantity": 1,
      "price_cents": 2999
    }
  ],
  "payment_type": "subscription",
  "subscription": {
    "interval": "monthly",
    "interval_count": 1,
    "trial_period_days": 7
  }
}

Customers will see subscription terms in the checkout and agree to recurring billing.

Customization

Iframe Styling

#gale-checkout {
  width: 100%;
  max-width: 800px;
  height: 650px;
  border: 1px solid #e5e7eb;
  border-radius: 12px;
  box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

/* Responsive */
@media (max-width: 768px) {
  #gale-checkout {
    height: 700px;
  }
}

Success/Cancel URLs

Customize where customers land after checkout:

{
  "success_url": "https://yoursite.com/thank-you?session_id={CHECKOUT_SESSION_ID}",
  "cancel_url": "https://yoursite.com/checkout/cancel"
}

Variables available:

{CHECKOUT_SESSION_ID} - Checkout session identifier
{ORDER_ID} - Order identifier (after payment)
{CUSTOMER_EMAIL} - Customer’s email

Platform Integration Examples

Multi-Tenant Platform

// Create checkout for specific merchant/store
const createMerchantCheckout = async (merchantId, storeId, checkoutData) => {
  const response = await fetch('https://api.withgale.com/v2/checkout', {
    method: 'POST',
    headers: {
      'Authorization': `Bearer ${getMerchantApiKey(merchantId)}`,
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      ...checkoutData,
      metadata: {
        merchant_id: merchantId,
        store_id: storeId,
        platform: 'your_platform_name'
      }
    })
  });

  return response.json();
};

Shopify App Example

// Shopify app creating embedded checkout
app.post('/shopify/create-checkout', async (req, res) => {
  const { shop, cart } = req.body;

  // Create Gale checkout session
  const galeCheckout = await fetch('https://api.withgale.com/v2/checkout', {
    method: 'POST',
    headers: {
      'Authorization': `Bearer ${getShopApiKey(shop)}`,
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      customer: {
        email: cart.customer.email,
        first_name: cart.customer.firstName,
        last_name: cart.customer.lastName,
        phone: cart.customer.phone
      },
      line_items: cart.lineItems.map(item => ({
        merchant_product_id: item.id,
        name: item.title,
        price_cents: Math.round(item.price * 100), // Convert to cents
        quantity: item.quantity
      })),
      metadata: {
        shopify_cart_id: cart.id,
        shop: shop
      }
    })
  });

  const checkout = await galeCheckout.json();
  res.json({ checkout_url: checkout.checkout_url });
});

Security Best Practices

Verify Webhooks

Always verify webhook signatures before processing

Use HTTPS

Only embed checkout on HTTPS pages

Validate Origins

Check event.origin in postMessage listeners

Secure API Keys

Never expose API keys in frontend code

Testing

Test Mode

Use test API keys for development:

Authorization: Bearer glm_test_YOUR_TEST_KEY

Test the Flow

Create a test cart
Embed checkout iframe
Use test HSA card: 4111111111111111
Complete payment
Verify webhook received

See all test cards →

Troubleshooting

Iframe not loading

Possible causes:

Incorrect checkout_url
Missing allow="payment" attribute
HTTPS required
Content Security Policy blocking iframe

Solution: Check browser console for errors, ensure HTTPS, add CSP exception

Not receiving postMessage events

Solution: Verify origin check matches https://checkout.withgale.com exactly

Checkout shows 'Session Expired'

Solution: Checkout sessions expire after 24 hours. Create a new checkout session.

Mobile iframe issues

Solution: Some mobile browsers have iframe limitations. Consider using redirect flow (payment links) for mobile.

API Reference

Complete API documentation:

Next Steps

Webhooks Setup

Configure real-time payment notifications

Custom API

Need more control? Try custom API integration

Subscriptions

Learn about subscription management

Test Cards

Test your integration with test HSA cards

Support

Questions about embedded checkout?

Getting Started

Integration Guides

Core Objects

Checkout

Payment Links

Orders

Products

Subscriptions

Webhooks & Errors

​Embedded Checkout Integration

​When to Use Embedded Checkout

​How It Works

​Implementation Steps

​Step 1: Create Checkout Session

​Step 2: Embed Checkout

​Step 3: Handle Payment Confirmation

​Option A: Webhooks (Recommended)

​Option B: PostMessage Events

​Option C: Polling (Not Recommended)

​Subscription Support

​Customization

​Iframe Styling

​Success/Cancel URLs

​Platform Integration Examples

​Multi-Tenant Platform

​Shopify App Example

​Security Best Practices

Verify Webhooks

Use HTTPS

Validate Origins

Secure API Keys

​Testing

​Test Mode

​Test the Flow

​Troubleshooting

​API Reference

​Next Steps

Webhooks Setup

Custom API

Subscriptions

Test Cards

​Support

Embedded Checkout Integration

When to Use Embedded Checkout

How It Works

Implementation Steps

Step 1: Create Checkout Session

Step 2: Embed Checkout

Step 3: Handle Payment Confirmation

Option A: Webhooks (Recommended)

Option B: PostMessage Events

Option C: Polling (Not Recommended)

Subscription Support

Customization

Iframe Styling

Success/Cancel URLs

Platform Integration Examples

Multi-Tenant Platform

Shopify App Example

Security Best Practices

Testing

Test Mode

Test the Flow

Troubleshooting

API Reference

Next Steps

Support