I need a developer who can streamline our cross-platform experience. When someone browses our website on a phone that already has the app installed, the session should jump straight into the relevant screen in the Android or iOS app. If the app is missing, I still want the visitor to see a friendly prompt with the choice to open the App Store or simply stay on the web page. Inside the app, a separate fix is required: certain flows currently attempt to hand control to an external e-commerce app and trigger a PAYU gateway error. I need that intent or universal-link hand-off to work smoothly every time, without breaking the payment chain. Finally, I want to reach out to users who have not yet installed the app. A lightweight notification or banner triggered by Firebase, OneSignal, or a similar push service is fine so long as it reliably targets only those who are still web-only visitors. Deliverables • Functional universal links / Android App Links for both iOS and Android • Clean fallback logic for non-installed users (prompt + correct store link) • Stable in-app redirection to the specified e-commerce app with no PAYU errors • Push or in-browser notification set-up to nudge web-only users to install the app • Short walkthrough or README so my team can test and verify the flows Acceptance is based on end-to-end testing: website → app (installed and not installed scenarios), app → external e-commerce app with successful PAYU completion, and targeted install prompt delivery.