You will start seeing ads in Facebook Messenger in the coming months
In addition to monetizing the messaging aps, these advertisements are supposed to help users discover brands and businesses relevant to their interests. When the trial is finished, any advertiser in the world will have the option of purchasing ad space in Messenger, and increasingly more users around the globe will be able to see the ads. They will look something like this:
Tapping on an ad takes you straight to the product page. In addition to traditional ads, Facebook envisions "Click to Messenger ads" that take users to the app and spark a conversation, along with sponsored messages with which businesses are able to reach out to users that previously interacted with them.
Overall, Facebook seems to be smart with bringing this type of monetization to Messenger. Ads will only appear in the Home screen and won't show up in conversations. Furthermore, users will be given the choice to hide and report certain ads, not unlike the Facebook app experience.