What you pay for
You only pay for the engagements you acquire from your campaign. The cost-per-engagement model applies to initial engagements (such as replies, likes, Quote Tweets, and Retweets) on your Promoted Tweets. You’re not charged for any organic engagements that follow, nor engagement on non-Promoted Tweets.
The cost you pay per engagement depends on your set budget and bid, as well as your targeting. You'll receive real-time bid guidance during the setup process.