The advert with lies was, according to the article (it has links to other articles, check "advertising campaign" in the first paragraph, leading you here: https://www.nytimes.com/2019/10/08/technology/facebook-trump-biden-ad.html):

The 30-second video ad released by the Trump campaign last week is grainy, and the narrator’s voice is foreboding. Former Vice President Joseph R. Biden Jr., it says, offered Ukraine $1 billion in aid if the country pushed out the man investigating a company tied to Mr. Biden’s son.

Though this article focuses on the fact that Facebook did:

Facebook took the highly unusual step of tweeting a public response to Warren by name, comparing itself to a local broadcaster who is required by law to carry political ads, and even citing Federal Communications Commission rules as a rationale.