Call this method from the main thread to fetch deferred applink data if you use Mobile App Engagement Ads (https://developers.facebook.com/docs/ads-for-apps/mobile-app-ads-engagement). This may require a network round trip. If successful, the handler is invoked with the link data (this will only return a valid URL once, and future calls will result in a nil URL value in the callback).
The handler to be invoked if there is deferred App Link data
The handler may contain an NSError instance to capture any errors. In the common case where there simply was no app link data, the NSError instance will be nil. This method should only be called from a location that occurs after any launching URL has been processed (e.g., you should call this method from your application delegate's applicationDidBecomeActive:).
Describes the callback for fetchDeferredAppLink.
typedef void (^FBSDKDeferredAppLinkHandler)(NSURL *url,NSError *error);
The url may also have a fb_click_time_utc query parameter that represents when the click occurred that caused the deferred App Link to be created.