
Facebook has Instant Articles that are aimed to make articles posted on its platform better and faster when viewed on mobile, if compared to the web's standard version of pages.
For better or worse, the social giant is adding a below-the-fold advertisement slots on its Instant Articles pages.
In June 8th, 2017, the company announced that all Instant Articles publishers can feature ads within "Related Articles" section, appearing below their actual articles. Facebook started testing these ads since March 2017, and claimed to see an "incremental increase" in the amount of money publishers can make per thousand page views.
Those below-the-fold ads are "native" ads, even though they're actually not.
Below is an example that Facebook included in its blog post:

The ads appear to be the same photo and link ads that Facebook typically show in people's News Feed. The difference is that they're placed among a feed of links.
In order to feature an advertisement inside an Instant Article's "Related Articles", publishers need to be part of Facebook's Audience Network that Facebook uses to syndicate its News Feed ads across an ad network of third-party websites and apps.
When the publishers have configured their Instant Articles to feature these ads, they can then select the "Banner" type as the format.
According to a Facebook's spokesperson, there are no requirements to add an ad link to a piece of content. The only thing publishers should do, is to make that advertisement links to a landing page, which can be any URL. Ads are limited to photo-and-link formats, so there aren't the option to choose native videos that play inline.
Advertisers that buy Instant Articles ad from Facebook, aren't given the permission to control how their ads appear within the "Related Articles" section. But they can still choose whether to run in Instant Articles or not, and can also block specific publishers or categories in they want to.