To accurately measure ROI from Google Ads campaigns in your OpenCart store, it’s essential to implement conversion tracking using Google Tag Manager (GTM). When users complete a purchase, a conversion should be recorded and tied back to their ad click.

✅ What This Implementation Tracks

Metric	Description
Conversion	When a purchase is completed
Conversion Value	Total revenue from order
Transaction ID	Unique order reference to prevent duplicates
Currency	Currency used for the purchase

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🧰 Requirements

• OpenCart admin + FTP access
• GTM container installed in OpenCart
• Google Ads account with a conversion action created
• Google Ads Conversion ID and Label
• Basic PHP + Twig editing capability

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🚀 Step-by-Step: Google Ads Conversion Tracking in OpenCart via GTM

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🔹 Step 1: Create a Google Ads Conversion Action

1. Go to your Google Ads account
2. Navigate to Tools & Settings → Conversions
3. Click + New Conversion Action
4. Choose Website
5. Enter conversion settings:
   • Category: Purchase
   • Conversion name: Purchase Conversion
   • Value: Use different values for each conversion
   • Count: One per conversion
   • Click-through window: 30 days
6. Click Create and Continue
7. Select Use Google Tag Manager
8. Note down:
   • Conversion ID: e.g., AW-123456789
   • Conversion Label: e.g., XyZAbc1234

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🔹 Step 2: Inject Dynamic Conversion Data into dataLayer in OpenCart

Edit catalog/controller/checkout/success.php:

$order_id = $this->session->data['order_id'];
$this->load->model('checkout/order');
$order_info = $this->model_checkout_order->getOrder($order_id);

$data['google_ads_conversion'] = json_encode([
  'event' => 'purchase',
  'transaction_id' => $order_info['order_id'],
  'value' => $order_info['total'],
  'currency' => $order_info['currency_code']
]);

Now edit success.twig (usually located in catalog/view/theme/YOUR_THEME/template/checkout/):

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

✅ This pushes the conversion event into the dataLayer only after a successful purchase.

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🔹 Step 3: Create GTM Data Layer Variables

In your GTM container, go to Variables → New → Data Layer Variable and create:

Name	Data Layer Variable
DLV - transaction_id	transaction_id
DLV - value	value
DLV - currency	currency

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🔹 Step 4: Create the Conversion Trigger

Go to Triggers → New

• Trigger Type: Custom Event
• Event Name: purchase
• Trigger fires on: All Custom Events
• Name it: Event - Purchase

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🔹 Step 5: Add Google Ads Conversion Tag in GTM

1. Go to Tags → New
2. Tag Type: Google Ads Conversion Tracking
3. Fill in:
   • Conversion ID: from Step 1
   • Conversion Label: from Step 1
4. Click Enable value tracking
5. Set:
   • Conversion Value: {{DLV - value}}
   • Transaction ID: {{DLV - transaction_id}}
   • Currency Code: {{DLV - currency}}
6. Trigger: Event - Purchase
7. Save and name: Google Ads Conversion - Purchase

✅ This tag fires when the purchase event is pushed to the dataLayer with value and transaction ID.

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🔹 Step 6: (Optional) Setup Enhanced Conversions via CSS Selectors

If you want to enhance conversion data using email or phone number from checkout, you can add Enhanced Conversions:

1. In GTM, create a variable:
   • Type: DOM Element
   • Selector: input[name="email"]
   • Attribute: value
2. In your Google Ads Conversion Tag:
   • Enable Enhanced Conversions
   • Select Email variable

This is optional but improves attribution accuracy.

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🔹 Step 7: Test Everything in GTM & GA

1. Enable GTM Preview Mode
2. Place a test order in your OpenCart store
3. Confirm the purchase event appears in Preview mode
4. Confirm Google Ads Conversion Tag fires
5. Use Google Tag Assistant to validate tag
6. In Google Ads → Conversions → Status: check for incoming conversions within 24 hours

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🔄 Optional: Deduplicate Conversion Events in GA4 + Google Ads

If you’re also sending purchase data to GA4 and importing conversions, deduplicate using:

• Matching transaction_id
• Mark one conversion source as primary

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📊 Summary Table

Step	Action
1	Create conversion in Google Ads
2	Inject conversion data in dataLayer on success page
3	Create GTM variables for transaction_id, value, currency
4	Add custom event trigger for purchase
5	Configure Google Ads conversion tag with dynamic values
6	(Optional) Add Enhanced Conversions
7	Test with Tag Assistant and debug tools

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