My Flutter + Firebase app is already live on Google Play with an active subscription model. I now need to introduce a 3-day free-to-use period that applies only to brand-new users; everyone who has ever subscribed or even opened the app before must continue on the current paid flow without interruption. I do not want any in-app, push, or email notifications for this change—the trial should simply expire after 72 hours, redirecting the user to the existing subscription screen. Scope of work • Update the Flutter client and Firebase backend so first-time installs automatically start a single, non-renewable 3-day trial. • Ensure Play Console subscription settings and server-side checks remain compliant with Google billing guidelines. • Preserve all current subscription logic for returning or already-paying users. • Provide clear build instructions and a brief summary of code changes so I can publish the updated APK/AAB myself. Acceptance criteria – A new user can access all premium features for exactly 72 hours from first launch. – After the free window ends, the standard paywall is shown with no loopholes. – Existing users’ subscriptions stay untouched. – All changes compile cleanly in the latest stable Flutter and run on Android 12+.