Rewarding users for reviewing your app may be perceived as trying to manipulate reviews, even if everyone receives a reward regardless of what rating or review they leave. Such behaviour is prohibited by Apple’s developer guideline 5.6.3. There’s another rule that states “Apps must not force users to rate the app, review the app, download other apps, or other similar actions in order to access functionality, content, or use of the app.”, see 3.1.1(a). Giving someone a reward for leaving a review could be seen as giving them access to content.
TLDR; don’t incentivise users to rate/review your app.
As for the callback feature, I believe Apple doesn’t let the developer know anything about the review process. You can request the review prompt, but whether or not Apple shows it or what the user does is hidden from the developer.