HTML in-app messages can call the SDK from JavaScript. See JavaScript Bridge for HTML In-Apps.
In-App Messages in iOS
Display contextual in-app messages in your iOS app and handle deep links and custom actions.
In-app messages appear while a user is active in your app, which makes them useful for contextual prompts, cross-sell, and onboarding. The SDK renders the message; your app controls where messages are allowed to show and what happens when a user taps one.