Action Details
Requirements and how-to articles for Google Ads's action:

Matched Content is a free recommendation service that offers you a simple way to promote your content to your site visitors. By offering your readers more content that's relevant to them, you can increase your site's page views, the time spent on your site, reader loyalty, ad impressions and ultimately ad revenue.

Requirements
You need this to get it done:

Check Eligibility
Matched Content is available to select publishers. To use Matched Content, you must have a site that meets Google's minimum requirements for traffic volume and number of unique pages. You can find out if your site is eligible for Matched Content by checking the "Sites" page in your AdSense account. If your site is eligible, you may place Matched Content units on any of its pages.
Ad Unit Name
The internal name for your Matched Content unit.
Font
Set the font for all of the text in your Matched Content unit. You can choose from a range of Google fonts.
Title Colour
Choose the font colour for the title of your unit.
URL Colour
Choose the font colour for the URL in your unit.
Size
You can choose between responsive size and custom size for your unit.
Ad Options
Google recommends leaving "Monetise with ads" switched on unless you'd prefer not to show ads in your Matched Content unit.
Code Snippet
Once you are finished designing your Matched Content unit, click "Save and Get Code" and Google will provide you with an HTML code snippet to copy and paste in between the <body> and </body> tags of the code for your chosen page(s) on your site.
Requirements missing or found errors? Report

How-To Articles
A list of useful links for you:

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AdSense Help - About Matched Content
Information about Matched Content.
Official
Link missing here or found errors? Improve How-Tos