In a modern OpenCart setup, events like purchase, add_to_cart, and view_item are sent to multiple platforms—GA4, Meta (Facebook) Conversions API, and TikTok Events API. Without proper deduplication, you’ll face:

• Over-reported conversions
• Skewed attribution
• Broken ROAS metrics

🎯 Platforms Covered

Platform	Deduplication Key
GA4	Automatic w/ event_id
Meta CAPI	event_id (critical)
TikTok CAPI	event_id (optional but preferred)

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🧰 Prerequisites

• OpenCart v3.x or v4.x
• Web GTM + Server GTM (for Meta/TikTok CAPI)
• GA4 Configured via GTM
• Meta Pixel + CAPI
• TikTok Pixel + Events API setup
• Consent Management (optional)

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📦 Step 1: Generate & Push a UUID for Deduplication

In your OpenCart success.twig (on purchase confirmation):

Add This Script to Push event_id:

<script>
(function() {
  function uuidv4() {
    return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
      var r = Math.random() * 16 | 0,
          v = c === 'x' ? r : (r & 0x3 | 0x8);
      return v.toString(16);
    });
  }

  const eventID = uuidv4();
  window.dataLayer = window.dataLayer || [];

  dataLayer.push({
    event: 'purchase',
    event_id: eventID,
    transaction_id: '{{ order_id }}',
    value: {{ total }},
    currency: '{{ currency }}',
    items: [/* product loop data here */]
  });

  // Store event ID in a cookie or localStorage for server use
  localStorage.setItem('event_id_purchase', eventID);
})();
</script>

✅ event_id is generated once and used across GA4, Meta Pixel, and TikTok tracking layers.

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🧪 Step 2: GA4 Tag with event_id for Purchase

In GTM:

• Event: purchase
• Add custom parameter:
  • Name: event_id
  • Value: {{DLV - event_id}}
    (Create a Data Layer Variable)

GA4 automatically supports event_id deduplication.

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🔗 Step 3: Meta Pixel + Meta CAPI with Deduplication

A. Meta Pixel Tag (Client-side)

• Event: Purchase
• Parameter:
  • eventID: {{DLV - event_id}}

Make sure you are explicitly sending eventID to Pixel.

B. Meta CAPI (Server-side GTM)

Use a GA4 → Server → Meta CAPI flow.

• Create Meta CAPI tag in Server GTM
• In the request template:{ "event_name": "Purchase", "event_time": {{Timestamp}}, "event_id": {{event_id}}, "user_data": { "em": {{hashed_email}}, "ph": {{hashed_phone}} }, "custom_data": { "value": {{value}}, "currency": "{{currency}}" } }
• Retrieve event_id from client via event_id_purchase in cookies or HTTP header.

⚠️ Must match exact value from the client for deduplication to work.

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🎯 Step 4: TikTok CAPI Deduplication

TikTok doesn’t require event_id strictly, but recommends it for de-duping against pixel events.

A. TikTok Pixel (Client-Side)

• Fire Purchase event
• Pass event_id: {{DLV - event_id}} into advanced matching

B. TikTok Events API (Server-Side)

In Server GTM or middleware, include event_id:

{
  "event": "Purchase",
  "timestamp": "{{Timestamp}}",
  "event_id": "{{event_id}}",
  "properties": {
    "pixel_code": "YOUR_PIXEL_ID",
    "user": {
      "email": "{{hashed_email}}"
    },
    "contents": [...],
    "currency": "USD",
    "value": 200
  }
}

Use a lookup variable or cookie to extract event_id on the server.

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🧰 Step 5: Server-Side Retrieval of event_id

Option A: Via Client Cookie → Request Header

Client JS:

document.cookie = "event_id_purchase=" + eventID + "; path=/";

In Server GTM:

• Use {{Cookie - event_id_purchase}}

Option B: Via x-event-id Header

Send event_id using a custom request header in fetch/XHR if your OpenCart has custom integrations.

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📊 Step 6: Reporting Use Cases

Report Type	Platform	Metric Example
Deduped Purchase Events	Meta Ads	Events matched = 100%, Deduplicated = 50%
Conversion Matching	TikTok Ads	event_id match status in TikTok Manager
GA4 Attribution	GA4	Clean funnel tracking by event ID

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🔐 Consent Integration (Optional)

Wrap deduplication script in consent check:

if (window.Cookiebot && Cookiebot.consents.given.analytics) {
  // execute uuid generation + dataLayer.push
}

Or set server-side triggers to only fire with consent=true.

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🧠 Pro Tips

• Always log event_id with order data in your backend DB for reconciliation
• Use the same timestamp granularity (epoch seconds) across systems
• Avoid multiple event_id generations for the same action

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