Jonathan Tzou, director of marketing at GSV Labs, screenshotted a promotion for Uber that appeared at the top of his Messenger app:
Facebook-A  £110.67
Facebook-A+/-+0.78%+0.70
Disclaimer
TechCrunch's Josh Constine and Jon Russell reported that when Facebook rolls out Messenger ads it will be in the form of allowing businesses that already have chat threads with consumers to send them messages with sale announcements or product information. 
Tzou has never used Uber through Messenger before, and this promotion wasn't in a message thread, so it's unclear whether this is another kind of ad that Facebook is thinking of using broadly or something that is exclusive to Uber. 
The ride-hailing app started integrating with Facebook Messenger in December, but consumer usage of the feature has been slow, sources told The Information's Cory Weinberg reported earlier this month
So, there's also a chance that this could be a non-paid relationship between Uber and Facebook, too, as the social network tries to encourage developers who are considering plugging into the Messenger platform.
Neither Facebook nor Uber could be reached for comment.