A series of messages is a great way to continually try and move a user towards a specific goal. That goal can be a purchase, signup, to re-engage in any way. Once that goal is achieved you want the messages to stop sending, especially if there are further incentives like larger discounts. The guide will show you how to set up the exit criteria for a campaign series.
Adding an Exit to a Campaign Series
Adding an exit is only available once you have multiple messages. If you want to measure a single touchpoint campaign's performance against a specific goal, you can do that by Setting A Different Attribution Goal.
Exits happen either by someone timing out (they are no longer reachable or don't match future content qualification) or have achieved a goal. These goals can be anything that you can define with a Filter. Most of the primary conversions are all set up already in your account. You can apply or change a goal as shown here: