Link insertion is paying the owner of an existing article to add a link to your website inside it. The article is already published and already indexed, so the link looks earned. It is also called a niche edit. Google classes any link bought to pass ranking credit as a link scheme, whatever it is called.
It shows up in proposals as link acquisition, authority placements or a price per link. The fact that there is a price per link is the tell.
A paid or sponsored link should carry rel="sponsored" (or at least rel="nofollow") so it passes no ranking credit; that is the only form of paid placement Google permits. A link insertion sold as SEO is by definition one left unmarked, so it passes credit and counts as a scheme. If you inherit a profile of them, document each with the vendor and date, request removal or a rel="sponsored" edit and treat the disavow file as the last resort, not the first.
<a href="https://example.com/" rel="sponsored">anchor text</a> 