Google Ads CAPI

1Role / Purpose

Google Ads Enhanced Conversions is the server-side destination for Google Ads conversions. It occupies a specific place in the stack:

Shopify Store
  ↓
GTM Web (DataLayer + Consent Mode v2)
  ↓
GA4 (technical transport)
  ↓
sGTM (Server-Side GTM)
  ↓
┌─────────────────────────────────────┐
│  GADS – Conv – purchase (sGTM tag)  │  ← This guide
│  Enhanced Conversions enabled        │
│  Automatic SHA-256 hashing           │
└─────────────────────────────────────┘
  ↓
Google Ads Conversions API

This setup delivers:

• 100% server-side Google Ads tracking
• Strict GDPR compliance (EU consent mandatory)
• Better resilience against adblockers
• Improved attribution through Enhanced Conversions
• Deterministic deduplication

2Overall Architecture

Full data flow

Cookiebot (EU CMP)
      ↓
GTM Web (Consent Mode v2 + DataLayer)
      ↓
GA4 (technical transport only)
      ↓
Server-Side GTM (sGTM)
      ↓
Addingwell Google Ads template
      ↓
Google Ads Conversions API

sGTM routing

The sGTM container receives the GA4 events and routes them to each destination. Google Ads is one of them:

sGTM (server)
→ GA4 Client (receives the request)
  ├── GA4 Server tag → Google Analytics 4
  ├── META – CAPI – All Events → Meta (Full CAPI)
  ├── GADS – Conv – purchase → Google Ads Enhanced Conversions  ← This guide
  └── (coming soon) TikTok Events API, Snap CAPI

Core principles

• No Google Ads tag directly in the theme
• No duplicate client + server conversion
• One purchase source only: the GTM Web dataLayer
• Consent required before anything is sent
• GA4 used as technical transport
• The Remarketing tag stays client-side for audiences

Single source of conversions

Every conversion comes exclusively from:

GTM Web → dataLayer purchase → GA4 event → sGTM

3Enhanced Conversions in Detail

Enhanced Conversions architecture

Enhanced Conversions (EC) is enabled by default on the sGTM tag GADS – Conv – purchase. User data is hashed server-side automatically by Addingwell, with no manual step.

Data sent (first-party)

The following is collected after consent and hashed SHA-256 server-side before reaching Google:

• Email (SHA-256 hash)
• Phone (SHA-256 hash)
• Optionally first / last name (SHA-256 hash)
• Address (SHA-256 hash)

How EC improves matching

Google uses this hashed data to match the conversion back to the original Google Ads click, even when the gclid cookie is missing or expired. The match rate rises significantly, which means better attribution and more efficient bidding.

Without EC:
Google Ads click → gclid cookie → purchase → Match (if cookie present)

With EC:
Google Ads click → gclid cookie → purchase → Match via gclid
                                           → Match via email (hash)
                                           → Match via phone (hash)
                                           → Match via address (hash)

= Higher match rate, even without a cookie

Server-side hashing

4Events & Parameters

Primary conversion

Parameters forwarded

• transaction_id
• value
• currency
• items (when needed)
• gclid / wbraid / gbraid
• hashed user_data (Enhanced Conversions)

5Deduplication Logic

Global unique identifier

transaction_id = conversion_id

The same identifier is used for:

• GA4 purchase
• Google Ads conversion
• sGTM logs

Rules

• One purchase in the dataLayer, and only one
• No second client-side Google Ads send
• No double mapping in the sGTM
• No conversion imported in parallel

6Google Attribution Identifiers

Attribution cookies (first-party)

Attribution cookies are persisted first-party by Addingwell (cookie restore), surviving Safari ITP and browser purges:

Forwarding to the server

1. 1Read in GTM Web
2. 2Injected into the GA4 event
3. 3Forwarded to the sGTM through the first-party transport
4. 4Injected into the Addingwell Google Ads template

7Configuration

Required credentials

sGTM tag

The GADS – Conv – purchase tag is configured in the sGTM container through the Addingwell template. Enhanced Conversions is on by default.

Enhanced Conversions in Google Ads

1. 1Go to Google Ads > Conversions > Settings
2. 2Enable "Enhanced Conversions"
3. 3Pick "Google Tag Manager" as the method
4. 4Check that diagnostics confirm the data is arriving

8EU Consent

Consent is handled exclusively through:

Cookiebot + GTM Consent Mode v2

Signals Google Ads requires

9Verification

Where to check

1. 1Google Ads > Conversions > Diagnostics: check that Enhanced Conversions are being received
2. 2Google Ads Tag Assistant: validate the conversion tag and EC
3. 3sGTM Preview — confirm the GADS – Conv – purchase tag fires
4. 4DevTools > Application > Cookies: check that the gclid, wbraid and gbraid cookies are present

Phase 3: Google Ads checklist

Google Ads-specific verification, lifted from the full QA process:

10Reading the Google Ads Metrics

Why conversions sometimes differ from clicks

Expected causes:

• Consent declined
• Multi-device users
• Cookie blocking
• Attribution delays
• Modelled conversions

Why GA4 ≠ Google Ads

11Metrics You Can Optimise On

The KPIs worth watching:

• Cost per Conversion
• ROAS
• Conversion Value
• Post-consent conversion rate
• Server-side conversion volume

12Responsibilities Matrix

13Troubleshooting

14Checklist

Weekly media-buyer checklist

Every week, check: