A deep link is a URL that opens a specific screen inside an installed app, such as an order or a boarding pass, rather than a website's front page.
Deep links in RCS
An RCS suggested action of the open-URL kind can carry a deep link, and the handset decides how to open it: in the app if it is installed and registered for that link, otherwise in the browser. Compared with the same link in an SMS, the RCS version is a labelled button under a verified sender, so the customer knows what it opens and who sent it before tapping. Android app links and iOS universal links both work; a custom scheme such as myapp:// only works where the app is installed and should have a web fallback.
When to use one
Whenever the action already lives in the app: track an order, check in, view a statement, approve a payment. A deep link removes the login and navigation steps that lose people on the way from a message to a task. When the customer may not have the app, link to the web page instead and let the page offer the app.
Measuring it
Each button tap returns an event to the sender with the postback data it was given, so click-through rate per button is available without instrumenting the app. What happens after the app opens is the app's analytics to report.