Dynamic Remarketing allows you to show personalized ads to users based on their past interactions—like viewing a product, abandoning the cart, or checking out. For OpenCart, the most scalable way to enable this is using Google Tag Manager (GTM) with GA4 eCommerce data.

✅ What This Setup Will Track

Event	Use in Remarketing
view_item	Show product-based ads
add_to_cart	Retarget cart abandoners
purchase	Exclude converters
view_item_list	List engagement-based retargeting

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🧰 Requirements

• OpenCart 3.x or 4.x access
• GA4 and GTM properly implemented
• Google Merchant Center linked to Google Ads
• Dynamic Remarketing feed approved
• Google Ads tag ID (e.g., AW-123456789)
• Product IDs in your OpenCart store match those in the Merchant Feed

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🚀 Step-by-Step: Dynamic Remarketing in OpenCart via GA4 Data

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🔹 Step 1: Format Product Data in GA4 Events

Update product and cart-related events in OpenCart to match Google’s dynamic remarketing parameters.

Example: Update catalog/controller/product/product.php

$product_id = (int)$this->request->get['product_id'];
$product_info = $this->model_catalog_product->getProduct($product_id);
$category = $this->model_catalog_category->getCategory($product_info['category_id']);

$data['gtm_view_item'] = json_encode([
  'event' => 'view_item',
  'ecommerce' => [
    'items' => [[
      'id' => $product_info['product_id'],
      'name' => $product_info['name'],
      'category' => $category['name'],
      'price' => $product_info['price']
    ]]
  ]
]);

In product.twig:

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

✅ This provides GA4-compliant product data that can also fuel remarketing.

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🔹 Step 2: Push Cart Events (add_to_cart, begin_checkout, etc.)

In catalog/controller/checkout/cart.php (for add_to_cart):

$data['gtm_add_to_cart'] = json_encode([
  'event' => 'add_to_cart',
  'ecommerce' => [
    'items' => [[
      'id' => $product_id,
      'name' => $product_name,
      'price' => $price,
      'quantity' => $quantity
    ]]
  ]
]);

Then output in the response view (cart.twig or AJAX template):

{% if gtm_add_to_cart %}
<script>
dataLayer.push({{ gtm_add_to_cart|raw }});
</script>
{% endif %}

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🔹 Step 3: Create Data Layer Variables in GTM

Create GTM Data Layer Variables to access GA4 eCommerce values:

Name	Key
DLV - item_id	ecommerce.items.0.id
DLV - item_category	ecommerce.items.0.category
DLV - item_price	ecommerce.items.0.price

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🔹 Step 4: Setup Google Ads Remarketing Tag in GTM

In GTM:

1. Go to Tags > New
2. Tag Type: Google Ads Remarketing
3. Enter your Google Ads Conversion ID (AW-XXXXXXXXX)
4. Choose: Use custom parameters
5. Enter the following key-value pairs:

ecomm_prodid: {{DLV - item_id}},
ecomm_pagetype: 'product',
ecomm_totalvalue: {{DLV - item_price}}

(For cart: pagetype = ‘cart’, for purchase: ‘purchase’)

6. Trigger: Use Custom Event trigger for view_item

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🔹 Step 5: Create Triggers for Each Event

GTM Trigger	Type	Event Name
Trigger - view_item	Custom Event	view_item
Trigger - add_to_cart	Custom Event	add_to_cart
Trigger - purchase	Custom Event	purchase

Link each to its respective Google Ads Remarketing Tag with the correct ecomm_pagetype.

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🔹 Step 6: (Optional) Send to Google Analytics 4

You can send the same view_item, add_to_cart, and purchase events to GA4 for reporting as well. Just create GA4 Event Tags with mapped parameters like:

items: [{
  item_id: {{DLV - item_id}},
  item_name: {{DLV - item_name}},
  item_category: {{DLV - item_category}},
  price: {{DLV - item_price}}
}]

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🔹 Step 7: QA with GTM Preview and Tag Assistant

1. Open GTM Preview mode
2. Navigate through product, cart, and checkout pages
3. Validate:
   • Correct event is pushed (view_item, add_to_cart, etc.)
   • Google Ads tag fires with right parameters
4. Use Google Tag Assistant → check that the ecomm_prodid and pagetype match page context
5. In Google Ads > Audience Manager > Data Sources, confirm tag is receiving hits

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🧠 Advanced: Page-Level Dynamic Parameters

For more precise control over dynamic remarketing:

Page	ecomm_pagetype
Homepage	'home'
Product page	'product'
Category	'category'
Cart	'cart'
Checkout	'checkout'
Purchase	'purchase'

Set this either in dataLayer or directly in tag parameter configuration.

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📦 Summary Table

Step	Action
1	Push GA4 eCommerce-compatible product data on product pages
2	Track cart interactions using add_to_cart events
3	Create GTM Data Layer Variables for item data
4	Add Google Ads Remarketing Tag using custom parameters
5	Trigger per event type (view_item, add_to_cart, etc.)
6	QA with GTM Preview + Tag Assistant
7	Confirm tag firing in Google Ads → Audience Sources

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