Coupon redemptions and discounted sales offer key insights into promotion performance, discount-driven buyers, and ROAS segmentation. Yet, many OpenCart setups fail to accurately send coupon usage data to Google Analytics 4 (GA4)—especially when multiple discounts are applied.

🧰 Prerequisites

Component	Purpose
OpenCart 3.x or 4.x	Storefront
Google Tag Manager	Installed across the site
GA4 Configured	Through GTM
Promo/Coupon Module	Default or custom

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🎯 What You’ll Track

• Coupon code used (e.g., SAVE20)
• Whether coupon was applied (binary)
• Final discounted revenue
• Optional: discount value in currency

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🧱 Step 1: Expose Coupon Info in Order Success Page

Edit the controller:
File: catalog/controller/checkout/success.php

Add This Logic:

if (isset($this->session->data['coupon'])) {
    $data['coupon_code'] = $this->session->data['coupon'];
} else {
    $data['coupon_code'] = '';
}

Then Pass It to the View:

Add $data['coupon_code'] into your success.twig file:

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🧾 Step 2: Push Purchase Data with Coupon to dataLayer

In your success.twig:

<script>
window.dataLayer = window.dataLayer || [];

dataLayer.push({
  event: 'purchase',
  ecommerce: {
    transaction_id: '{{ order_id }}',
    value: {{ total }},
    currency: '{{ currency }}',
    coupon: '{{ coupon_code }}',
    items: [
      {% for product in products %}
      {
        item_id: '{{ product.product_id }}',
        item_name: '{{ product.name | escape('js') }}',
        price: '{{ product.price }}',
        quantity: '{{ product.quantity }}'
      }{% if not loop.last %},{% endif %}
      {% endfor %}
    ]
  }
});
</script>

✅ This includes the coupon field as part of the GA4 purchase schema.

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🔧 Step 3: Configure GTM Variables

Go to GTM → Variables → New:

• Data Layer Variable: ecommerce.coupon
• Name it: DLV - ecommerce.coupon

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🎯 Step 4: Update GA4 Purchase Event Tag

In GTM, open your GA4 Purchase event tag and add these:

Event Parameters:

Parameter Name	Value
coupon	{{DLV - ecommerce.coupon}}

💡 Optional: Add more if you pass discount value or flags like coupon_used: true.

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🔍 Step 5: Register coupon as a Custom Dimension in GA4

In GA4 Admin → Custom Definitions:

• Click Create Custom Dimension
  • Name: Coupon Code
  • Scope: Event
  • Event Parameter: coupon

Now the coupon value will show up in GA4 Explorations, Funnel Reports, and Looker Studio dashboards.

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📊 Bonus: Add Discount Amount (Optional)

To track discount amount, extract from order totals.

In your controller (success.php):

$discount_total = 0;
foreach ($order_totals as $total) {
    if (strtolower($total['code']) === 'coupon') {
        $discount_total = abs($total['value']);
    }
}
$data['discount_value'] = $discount_total;

Then add to dataLayer:

discount: {{ discount_value }},

And send via GTM to GA4 as:

Parameter Name	Value
discount_value	{{DLV - discount}}

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🧪 Step 6: QA and Testing

Tool	What to Check
GTM Preview Mode	purchase event contains coupon field
GA4 DebugView	Check coupon parameter in purchase
DevTools Console	Run dataLayer and inspect contents

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📈 Use Cases in GA4

Use Case	How to Use
Segment by coupon code usage	Compare coupon != null vs null
ROAS by promo	Report conversions by coupon in Looker
Abandoned cart re-targeting	Filter users who used a coupon but didn’t buy
Identify high-performing campaigns	Match utm_campaign + coupon correlation

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🧠 Pro Tips

• Always sanitize coupon strings (no HTML/JS injection)
• Add a coupon_used: true boolean parameter for filtering
• Consider hashing coupon if using personal codes (e.g., email-based)

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