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 |
🧰 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 |
📦 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.
🛰️ Step 4: Setup ssGTM Tags for GA4 & Google Ads
GA4 Event Tag (in Server GTM)
- Event Name:
purchase,begin_checkout, oradd_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 |
📊 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 |