Integrate Firebase to Android app and debug app

I want to run 2 in-app purchase app on Google Play and Apple Store so I have bought a Flutter code in Codecanyon. This is best-selling code here now and the buyers reviewed that it's rather good with no bugs.

But I don't have skills to edit it in Android Studio so I Google and completed some tasks by the guidlines in the Documentations, but finally I still can't build APK. I think my integration between Firebase and app has errors, and maybe for my Android Studio setup and related plugins in my PC.

1. I want to find an experienced coder who will integrate Firebase to Android app, then debug code to find what wrongs and build me a APK file so that I can use it to submit Google Play.

2. After Android app is OK, I want you to do the samething to iOS app with my information as the Documentation said, build me the last file to submit Apple Store.

Please do 2 above tasks for me in the fastest time and reasonable price if you can. Any details will discuss in chat.

Thank you.