In a privacy-first era of ad tracking and analytics, client-side tracking alone is no longer enough. OpenCart stores often suffer from lost conversion data, especially due to:

• Cookie restrictions (iOS, browsers)
• Ad blockers
• Delayed pixel firing

Server-side tracking of checkout events solves these issues by passing key signals like begin_checkout, add_payment_info, and purchase directly from your server to platforms like Google Ads, GA4, Meta, etc.

✅ What You’ll Achieve

Event	Tracked Server-Side
begin_checkout	Yes
add_payment_info	Yes
purchase	Yes
Conversion Value	Accurate and secure
Email/Phone	Hashed PII for matching
Deduplication	Using event_id

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🧰 Prerequisites

Requirement	Notes
OpenCart (3.x / 4.x)	Theme + controller access
Web & Server GTM	Installed and connected
GA4, Google Ads, Meta Pixel	Ready with Measurement ID / Tag ID
HTTPS Domain	Required for sending hashed data
Optional: Consent Layer	To handle PII lawfully in the EU/US

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📦 Step 1: Add Checkout Step Events in Controller

Edit: catalog/controller/checkout/checkout.php

Add a push for begin_checkout when user lands on the checkout page:

$data['ss_begin_checkout'] = json_encode([
  'event' => 'begin_checkout',
  'event_id' => uniqid('ss_checkout_', true)
]);

Then in checkout.twig, inject:

{% if ss_begin_checkout %}
<script>
window.dataLayer = window.dataLayer || [];
dataLayer.push({{ ss_begin_checkout|raw }});
</script>
{% endif %}

Repeat similarly in catalog/controller/checkout/confirm.php:

$data['ss_add_payment_info'] = json_encode([
  'event' => 'add_payment_info',
  'event_id' => uniqid('ss_payment_', true)
]);

And inject into the appropriate confirmation step view template:

{% if ss_add_payment_info %}
<script>
window.dataLayer = window.dataLayer || [];
dataLayer.push({{ ss_add_payment_info|raw }});
</script>
{% endif %}

---

🧾 Step 2: Finalize purchase Event in success.php

In catalog/controller/checkout/success.php:

$order_id = $this->session->data['order_id'];
$order_info = $this->model_checkout_order->getOrder($order_id);
$products = $this->model_checkout_order->getOrderProducts($order_id);

$email = strtolower(trim($order_info['email']));
$phone = preg_replace('/\D/', '', $order_info['telephone']);

$items = [];
foreach ($products as $product) {
  $items[] = [
    'item_id' => $product['model'],
    'item_name' => $product['name'],
    'price' => $product['price'],
    'quantity' => $product['quantity']
  ];
}

$data['ss_purchase'] = json_encode([
  'event' => 'purchase',
  'transaction_id' => $order_id,
  'currency' => $order_info['currency_code'],
  'value' => $order_info['total'],
  'email' => hash('sha256', $email),
  'phone' => hash('sha256', $phone),
  'items' => $items,
  'event_id' => uniqid('ss_purchase_', true)
]);

In success.twig:

{% if ss_purchase %}
<script>
window.dataLayer = window.dataLayer || [];
dataLayer.push({{ ss_purchase|raw }});
</script>
{% endif %}

---

🚀 Step 3: Forward Checkout Events to ssGTM

In Web GTM, add a Custom HTML Tag:

<script>
fetch('https://gtm.yourdomain.com/event', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    event_name: '{{DL - event}}',
    event_id: '{{DL - event_id}}',
    email: '{{DL - email}}',
    phone: '{{DL - phone}}',
    transaction_id: '{{DL - transaction_id}}',
    value: '{{DL - value}}',
    currency: '{{DL - currency}}',
    items: {{DL - items}}
  })
});
</script>

Trigger: All Custom Events matching begin_checkout, add_payment_info, or purchase.

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🛰️ Step 4: Setup ssGTM Tags for GA4 & Google Ads

GA4 Event Tag (in Server GTM)

• Event Name: purchase, begin_checkout, or add_payment_info
• Measurement ID: From GA4
• Parameters:
  • event_id, transaction_id, value, currency, items

Google Ads Conversion Tag (Server)

• Conversion ID / Label
• Email / Phone (hashed)
• Event ID
• Value / Currency / Transaction ID

Deduplication: Use event_id across both web and server tags.

---

🔐 Step 5: Optional — Consent Compliance

In Web GTM, conditionally fire fetch tag only if consent is granted using:

if (window.gtag && gtag.get('consent', 'ad_storage') === 'granted') {
  // send fetch
}

---

✅ Step 6: Testing

Tool	Check
GTM Preview	Ensure event pushes occur
Server GTM Preview	Confirm forwarded data
GA4 DebugView	Look for real-time hits
Google Ads Tag Diagnostics	Check deduplication
Meta Events Manager (if implemented)	For CAPI validation

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📊 Benefits Recap

Feature	Benefit
Server-Side Purchase Tracking	Higher attribution accuracy
Hashed PII	Matches even when cookies fail
Event Deduplication	Prevents inflated metrics
Checkout Stage Monitoring	Funnel drop-off analysis
Ads Platform Integration	Better optimization and ROAS

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