Guide on fixing errors GTM server-side

This guide helps you debug Google Tag Manager (GTM) server-side tag errors reported by Code-Cube.io Tag Monitor. A server-side container gives you more information about errors than a client-side container, so you can often find the cause quickly.

What will you do?

• Find the error details in GTM server-side Preview mode
• Apply general server-side checks
• Fix common errors for Google Ads, Meta, TikTok, and Criteo tags

🔧 Requirements: Access to your GTM server-side container and the Code-Cube.io portal

• Step 1 – Find the error details
• Step 2 – General server-side checks
• Step 3 – Fix common errors per tag type
• Google Ads
• Meta (Facebook) Conversions API
• TikTok Events API
• Criteo
• Help us improve this guide
• Related pages

Step 1 – Find the error details

Seeing a high share of failed tags (more than 75%)? Open GTM server-side Preview mode and go to the Console tab. It shows more information about the specific error.

Step 2 – General server-side checks

1. Use the trigger type 'Custom' as little as possible. It's very generic, so it quickly causes errors
2. Want to fire on all events? Use the trigger type 'Custom Event' with a wildcard (.*) instead
3. Check the client. Make sure the client handling the event is implemented correctly
4. Inspect incoming event data. Use the Event Data tab in server-side Preview mode to see what data is actually received. Wrongly formatted or missing parameters are a common cause of failed conversions or missing events
5. Check client mappings. If events aren't handled correctly, check that the right GTM client (e.g. GA4 or HTTP) is active and matches the incoming requests

Step 3 – Fix common errors per tag type

Google Ads

• Conversion Linker failing? Make sure the region-specific settings are added to your server-side instance (for example, Cloud Run)
• Tag marked as failed while conversions are tracked? This is a known false error caused by a cookie prefix mismatch. See Google Ads failed for no reason for the fix

Meta (Facebook) Conversions API

1. Meta is very strict about event parameters. A failing Meta tag is usually caused by an event parameter without the right value
2. Using a variable for an event parameter? Always add a default value
3. Check the tag's trigger. If it fires on events you don't intend, the tag can't fill in all parameters and throws an error. See the general trigger tips in Step 2

TikTok Events API

1. TikTok is very strict about event parameters. A failing TikTok tag is usually caused by an event parameter without the right value
2. Using a variable for an event parameter? Always add a default value
3. Check that the tag's trigger is specific enough. If it fires on events you don't intend, the tag can't fill in all parameters and throws an error. See the general trigger tips in Step 2

Criteo

1. Check that all parameters are configured correctly
2. Using a variable for an event parameter? Always add a default value

Help us improve this guide

Need help with a specific error? Email support@code-cube.io.

Related pages

• Guide on fixing errors GTM client-side
• What is considered an error?
• Configure BigQuery data access: access your raw monitoring data
• Dashboard overview