Many marketers struggle with seeing fewer conversions in Google Analytics 4 (GA4) than in ad platforms—or vice versa. These discrepancies can lead to inaccurate ROI reporting, poor optimization decisions, and wasted ad spend.

---

🎯 Common Causes of Discrepancy

Reason	Description
Event Deduplication Failure	Events counted twice or ignored due to mismatched event_ids
Ad Blockers / iOS App Tracking	Block client-side scripts (only CAPI may fire)
Consent Restrictions	Tags not firing due to lack of user consent
GTM Trigger Misalignment	Client-side event doesn’t trigger across all platforms
Parameter Mismatch	Key values like transaction_id, email are missing in ad platform calls
Attribution Windows / Models	Platforms use different lookback windows or attribution logic
Time Zone Differences	GA4 uses site time; ad platforms may use UTC or account timezone

---

🧰 Step 1: Setup Unified Conversion Event in GTM

Choose a shared event like purchase, and ensure it’s pushed consistently:

<script>
(function() {
  const eventId = 'evt_' + Date.now();  // Use UUID in production

  window.dataLayer = window.dataLayer || [];
  dataLayer.push({
    event: 'purchase',
    event_id: eventId,
    transaction_id: '{{ order_id }}',
    value: {{ total }},
    currency: '{{ currency }}',
    email: '{{ email | lower | sha256 }}',
    phone: '{{ phone | sha256 }}'
  });

  localStorage.setItem('event_id_purchase', eventId);
})();
</script>

---

📊 Step 2: Confirm GA4 Event Tracking

GA4 Tag in GTM:

• Event Name: purchase
• Trigger: Custom Event = purchase
• Parameters:
  • event_id, transaction_id, value, currency

Debug:

• Use GA4 DebugView
• Confirm event fires once
• Confirm transaction_id and event_id are populated

---

🎯 Step 3: Validate Meta Pixel + CAPI Tracking

Pixel Tag (Client-Side):

• Fires on purchase event
• Includes eventID = {{DLV - event_id}}

Meta CAPI Tag (Server-Side):

• Passes same event_id, transaction_id, and value
• Match with em, ph, or external_id

Debug:

• Use Meta Events Manager
• Look for:
  • Event match quality (email/phone match)
  • Deduplication status
  • Timestamp alignment
  • Event count (client + server)

---

🎥 Step 4: Validate TikTok Pixel + Events API

TikTok Pixel (Client-Side):

• Event Name: CompletePayment
• Pass event_id + order info

TikTok CAPI (Server-Side):

• Same event_id, value, currency

Debug:

• Use TikTok Events Manager
• Check:
  • Signal source
  • Deduplication success
  • UTM/click_id match

---

🧾 Step 5: Validate Google Ads Tracking

Google Ads Tag:

• Use gtag/GTAG via GTM or Google Ads Conversion tag
• Parameters:
  • conversion_id, conversion_label
  • transaction_id, value, currency

Debug:

• Use Google Ads Conversion Debug Tool
• Check Chrome DevTools > Network tab > collect? hit
• Verify:

"transaction_id": "123456",
"value": 199.99

---

🧪 Step 6: Compare Raw Hit Data

Use tools to inspect outgoing hits:

Tool	Use Case
GA4 DebugView	See live browser GA4 events
Meta Pixel Helper + Events Manager	Inspect client & CAPI match status
TikTok Pixel Helper	Real-time TikTok event validation
Google Tag Assistant	Inspect Google Ads & GA4 events
DevTools > Network > Payload	See collect? requests and payload contents
Server GTM Logs	Monitor server-tag delivery, headers, event_ids

---

📏 Step 7: Match GA4 + Ad Platform Conversions

Compare across platforms:

Metric	GA4	Meta Ads	TikTok Ads	Google Ads
Conversions Today	95	105	93	99
% Match to GA4	100%	110%	98%	104%
Duplicates Detected	0	5	2	1

Look for:

• 10–20% mismatch is normal due to tracking limitations
• 30% = Tagging or duplication issue

---

🔍 Step 8: Identify Root Causes

Symptom	Likely Cause
Meta showing double conversions	Missing or mismatched event_id on Pixel & CAPI
TikTok showing zero server events	Event not reaching CAPI endpoint
GA4 lower than ad platforms	Client-side blockers or consent filtering
Google Ads showing wrong values	value or currency mismatch

---

🔧 Step 9: Fixes & Best Practices

• Always pass event_id to both client and server tags
• Use same transaction_id in GA4 + Ads + CAPI
• Set up consent-aware tag firing
• Store & retrieve event_id via cookie/localStorage consistently
• Track and log payloads for debugging audit trails

---

🔐 Consent Wrapping (if applicable)

For regions under GDPR/CCPA, ensure tags fire only after consent:

if (window.Cookiebot && Cookiebot.consents.given.marketing) {
  // fire pixels and dataLayer.push
}

Or use GTM’s Consent Initialization trigger types.

---