How to add Reviews Snippet using Google Tag Manager

Back in September 2019, Google announced that self-serving reviews are no longer allowed on search engine results.

Here is what Google said on its official blog:

Self-serving reviews aren’t allowed for LocalBusiness and Organization.

Reviews that can be perceived as “self-serving” aren’t in the best interest of users. We call reviews “self-serving” when a review about entity A is placed on the website of entity A — either directly in their markup or via an embedded 3rd party widget.