Google Ads - Understanding Errors and Warnings

This guide details how the three critical conversion tracking components work, their typical errors and how to fix them: Enhanced Conversions, Cart Data, and Consent Mode.

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1. Enhanced Conversions

Definition

Enhanced conversions allow you to send first-party data — such as email address, name or phone number — securely (hashed using the SHA256 algorithm) to Google.

Technical Operation

When a user converts, the tags capture this data from the form fields or the dataLayer, encrypt it, and transmit it to Google to match it with a Google user account.

Common Errors & Causes

• Unhashed data: Sending the email in plain text (blocked by Google for privacy reasons).

• Unstable CSS selectors: If you use automatic capture, a site design change can break the link with the form field.

• Null JavaScript variables: The data is sent before the user has finished filling in the form or before the thank-you page has loaded.

Verification method

• Tag Assistant: Check that the conversion event contains the enhanced_conversion_data object.

• Console: Inspect the Network tab to see whether the em (email) or ph (phone) parameters are present in the /conversions request.

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2. Conversions with Cart Data

Definition

This data layer transmits the granular details of the transaction: product IDs, quantities, unit prices and categories. It powers the profit and cross-sell reports.

Technical Operation

The conversion tag must include an items array following Google's standard schema (similar to that of GA4).

Common Errors & Causes

• ID Mismatch: The product ID sent by the tag (item_id) does not match the ID configured in the Google Merchant Center feed.

• Price format: Using commas instead of periods, or including the currency symbol (€) in a numeric variable.

• Missing data: The items array is empty when the conversion tag is called.

Business Impact

Without this data, Google cannot optimize your Performance Max or Shopping campaigns for actual profitability (gross margin), only for gross revenue.

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3. Consent Mode (Consent Mode V2)

Definition

Consent Mode is a communication mechanism between your cookie banner (CMP) and Google tags. It indicates whether the user has accepted or refused advertising tracking.

Technical Operation

It relies on two main signals introduced with V2 (mandatory in Europe since 2024):

1. ad_user_data: Permission to send user data to Google.

2. ad_personalization: Permission for remarketing.

Common Errors & Causes

• "Basic" vs "Advanced" status: Tags are blocked even before consent, preventing conversion modeling.

• Loading order: The gtag('consent', 'default', ...) command is called after the conversion tag has loaded.

• Missing signals: The cookie banner has not been updated to send the new V2 parameters.

Legal and Performance Impact

• Sanction: Limitation or suspension of the use of audience lists (Remarketing).

• Data loss: Google is unable to use AI to estimate the conversions of users who refused cookies.

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🛠 Global Verification Procedure

1. Debug phase: Use Google Tag Assistant.

2. Simulation: Complete a full customer journey up to the purchase confirmation page.

3. DataLayer validation: Check that the ecommerce object is properly structured with transaction_id, value, and items.

4. Google Ads audit: Go to Tools and Settings > Conversions, click on the relevant action and check the Diagnostics tab.