Clicking on the notification takes us to “Advertise on Facebook” page.

Facebook confirmed to WebProNews, that they’re testing “Advertise Popular Posts with Notifications” on select users.
We also noticed, Facebook is now testing reminder to finish the uncompleted Ads.
Here’s the screenshot:
Clicking on the prompt takes us to setting up the Advertisement.
Readers: Have you seen any notification like this in your timeline?
Yep! I saw it yesterday!