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GTM·Google Tag Manager·warning

Mixed Data Layer Versions

This container has Data Layer Variables configured on both Version 1 and Version 2. The two versions resolve nested dataLayer paths differently. Version 2 can read into nested objects like `ecommerce.value`, while Version 1 cannot. Mixed-version containers produce two variables that read the same path but return different values, which breaks downstream conversion tracking in ways that are very hard to debug.

CL
By Christopher LandaverdeCreator of AdLint · ad-tech tracking specialistUpdated

Why It Matters

When GTM's Data Layer Variable feature shipped, it only supported flat paths. That was Version 1. Version 2 was introduced to support modern e-commerce dataLayer shapes with nested objects and arrays. Most modern containers should use Version 2 everywhere. The problem is that GTM does not auto-migrate variables when you set up a new container. Old variables stay on Version 1 indefinitely, and new variables default to Version 2. So a single container can end up with `DLV - oldRevenue` on V1 (which cannot read `ecommerce.value` and resolves to undefined) and `DLV - newRevenue` on V2 (which reads the same path correctly). A conversion tag wired to the older variable reports zero; one wired to the newer reports the real value. The root cause is invisible because the variables look identical in the UI unless you open them.

How To Fix It

  1. In GTM, open Workspace → Variables → User-Defined Variables.
  2. Click each Data Layer Variable in turn and check the "Data Layer Version" field.
  3. Standardise on Version 2 unless a specific variable has a documented reason to stay on V1 (rare; usually a legacy tag that depends on V1 behaviour).
  4. After changing a variable from V1 to V2, complete a test event in Preview and confirm the variable still resolves to a non-empty value. Some legacy variables read top-level keys (e.g. `revenue`) rather than nested keys (`ecommerce.value`); upgrading to V2 should not break these, but verify.
  5. Publish only when every Data Layer Variable in the container is on a consistent, documented version.

Example

Configuration
Variable: DLV - ecommerce.value
Data Layer Variable Name: ecommerce.value
Data Layer Version: Version 2
For Your Client Report

GTM Data Layer Variables on mixed versions (Version 1 and Version 2) within this container. Google's GTM variable documentation, Data Layer Version 2 is required to read nested dataLayer paths such as `ecommerce.value`; Version 1 cannot resolve them. Mixed-version containers produce variables that read the same path but return different values, breaking conversion measurement in ways that are not visible in the GTM Tags screen. Fix: standardise every Data Layer Variable on Version 2 unless explicitly required otherwise, and verify resolution in Preview before publishing. Source: support.google.com/tagmanager/answer/6164391.

Drop this paragraph into your client deliverable. Sources back to the canonical platform documentation linked below.

References

  1. [1]Google Tag Manager. Variable types (Data Layer Variable)

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