CAPI Tracking for E-Commerce Brands

What is CAPI (Conversion API)?

CAPI (Conversion API) allows you to send conversion data directly from your server to Google, bypassing browser-based tracking entirely. Instead of relying on JavaScript tags that can be blocked, you upload conversion events via the Google Ads API.

CAPI vs Client-Side Tracking

Conversion Types Supported

• Click conversions — Purchases, signups, or leads that happen after an ad click (requires GCLID)
• Call conversions — Phone orders tracked through call tracking systems
• Store sales — In-store purchases attributed to online ad exposure
• Enhanced conversions — Conversions enriched with first-party customer data (email, phone, address)

Why CAPI Matters for E-Commerce

For Google Shopping advertisers, conversion data directly impacts Smart Bidding performance. Missing conversions means Google can't optimise effectively.

The Impact on Your Campaigns

Why Accurate Data Enables Profit Optimisation

Tracking accuracy isn't just about reporting — it directly impacts bid optimisation. When 30% of conversions are invisible to Google, Smart Bidding makes decisions on incomplete data. Profit-based bidding tools like ProfitClarity include a tracking accuracy setting that compensates for this loss, ensuring your ROAS targets account for conversions Google can't see. But the foundation is accurate data: CAPI ensures you capture the full picture.

Step 1: GCLID Capture & Storage

The GCLID (Google Click ID) is the critical link between ad clicks and conversions. When someone clicks your Google ad, a unique identifier is appended to the URL:

https://yourdomain.com/product?gclid=EAIaIQobChMI...

Enable Auto-Tagging

1. In Google Ads, go to Settings → Account Settings
2. Enable Auto-tagging
3. This automatically appends gclid to all ad click URLs

Capture GCLID on Your Site

Add this script to capture GCLIDs from URLs and store them for later use:

// GCLID Capture Script
(function() {
    const CONFIG = {
        GCLID_KEY: 'grow_gclid',
        EXPIRY_DAYS: 90
    };

    // Extract GCLID from URL
    function getGclidFromUrl() {
        const params = new URLSearchParams(window.location.search);
        return params.get('gclid') ||
               params.get('wbraid') ||  // iOS web fallback
               params.get('gbraid');   // iOS app fallback
    }

    // Store in localStorage + cookie
    function storeGclid(gclid) {
        if (!gclid) return;

        // localStorage (primary)
        localStorage.setItem(CONFIG.GCLID_KEY, gclid);
        localStorage.setItem(CONFIG.GCLID_KEY + '_ts', Date.now());

        // Cookie (backup, cross-subdomain)
        const expires = new Date(
            Date.now() + CONFIG.EXPIRY_DAYS * 86400000
        );
        document.cookie = CONFIG.GCLID_KEY + '=' + gclid +
            ';expires=' + expires.toUTCString() +
            ';path=/;SameSite=Lax;Secure';
    }

    // Initialize
    const gclid = getGclidFromUrl();
    if (gclid) storeGclid(gclid);
})();

Pass GCLID Through Checkout

Ensure the GCLID is captured with each order by adding a hidden field to your checkout form:

<!-- Add to checkout form -->
<input type="hidden" name="gclid" id="gclid_field">
<script>
    // Populate hidden field with stored GCLID
    document.getElementById('gclid_field').value =
        localStorage.getItem('grow_gclid') || '';
</script>

Store GCLID in Your Database

Add a GCLID column to your orders table:

-- Database schema addition
ALTER TABLE orders ADD COLUMN gclid VARCHAR(255);
ALTER TABLE orders ADD COLUMN conversion_uploaded_at TIMESTAMP;
ALTER TABLE orders ADD INDEX idx_gclid (gclid);

Step 2: Create Conversion Actions

Before uploading conversions, you need to set up conversion actions in Google Ads.

Create a Conversion Action

1. In Google Ads, go to Goals → Conversions → Summary
2. Click + New conversion action
3. Select Import → Other data sources or CRMs
4. Choose Track conversions from clicks
5. Configure your conversion action:

Get the Conversion Action ID

After creating the conversion action, note the Conversion Action ID — you'll need this for the API upload.

Step 3: Upload Conversions via API

With GCLIDs captured and conversion actions created, you can now upload conversions to Google Ads.

API Requirements

• Developer token — Request via Google Ads API Center
• OAuth 2.0 credentials — From Google Cloud Console
• Customer ID — Your Google Ads account ID (without dashes)
• Conversion Action ID — From the conversion action you created

Conversion Upload Payload

Each conversion requires these fields:

// Conversion data structure
{
    "gclid": "EAIaIQobChMI...",           // Required
    "conversion_action": "customers/123/conversionActions/456",
    "conversion_date_time": "2026-03-23 14:30:00+00:00",
    "conversion_value": 99.99,
    "currency_code": "USD",
    "order_id": "ORD-12345"              // Prevents duplicates
}

Upload Frequency Best Practices

Step 4: Enhanced Conversions

Enhanced conversions add first-party customer data to your conversion uploads, dramatically improving match rates and attribution accuracy.

User Identifiers to Include

• Email address — Most important, highest match rate
• Phone number — E.164 format (+1234567890)
• First name & last name
• Street address, city, state, postal code, country

Data Normalisation & Hashing

All user data must be normalised and hashed with SHA-256 before upload:

// Data normalisation and hashing
function hashAndNormalize(value) {
    // 1. Normalize: lowercase, trim whitespace
    let normalized = value.trim().toLowerCase();

    // 2. Special handling for Gmail addresses
    if (normalized.includes('@gmail.com')) {
        const [username, domain] = normalized.split('@');
        // Remove periods from username
        normalized = username.replace(/\./g, '') + '@' + domain;
    }

    // 3. Hash with SHA-256
    return crypto.createHash('sha256')
        .update(normalized)
        .digest('hex');
}

// Example: Hash email before upload
const hashedEmail = hashAndNormalize('John.Doe@Gmail.com');
// Result: SHA-256 hash of "johndoe@gmail.com"

Multi-Layered Matching

Enhanced conversions use multiple signals to match conversions:

1. Primary match — GCLID links to specific ad click
2. Fallback match — Email/phone matches to signed-in Google account
3. Cross-device recovery — User clicks on mobile, converts on desktop
4. Cookie deletion recovery — GCLID expired but email matches

Best Practices

Data Quality Checklist

• Unique order IDs — Prevents duplicate conversions
• Accurate values — Use actual order totals, not placeholders
• Correct timestamps — Include timezone (e.g., 2026-03-23 14:30:00+00:00)
• GCLID case preserved — Exact match required
• Multiple identifiers — Email + phone + address for best match rate
• 90-day retention — Store GCLIDs for full attribution window

Common Pitfalls to Avoid

• Don't modify GCLIDs — Store exactly as received
• Don't batch daily — Upload within minutes, not hours
• Don't skip error handling — Implement retry logic
• Don't ignore partial failures — Check API response for rejected conversions
• Don't upload test data to production — Use separate conversion actions for testing

Combine with Tag Gateway

Tag Gateway and CAPI work together as complementary layers:

Profit-Based Conversion Values

Most brands upload order revenue as the conversion value. But Smart Bidding then optimises for revenue, not profit — treating a 10% margin sale the same as a 60% margin sale.

MarginStack enables profit-based conversion values. Instead of uploading £99.99 (order total), upload £35.00 (actual profit based on COGS, fees, and return costs). Now Google's algorithms optimise for what actually matters: profit.

ProfitClarity provides a validation layer that reconciles uploaded conversions with backend order data and MarginStack costs — ensuring your conversion values accurately reflect real profit margins, not estimates.

Monitoring & Diagnostics

Key Metrics to Track

Google Ads Diagnostics

1. Go to Goals → Conversions → Summary
2. Click your conversion action
3. Check the Diagnostics tab for:

• Upload status and errors
• Match rate for enhanced conversions
• Data freshness indicators
• Recommended improvements

Implementation Roadmap

A practical timeline for implementing CAPI tracking:

Expected Results

• 15-25% increase in tracked conversions
• 5-17% improvement in Smart Bidding performance
• 80%+ match rate for GCLID + user identifier combinations
• Recovery of iOS/ad-blocker lost conversions