How I built a movie/TV/anime tracker with React Native, FastAPI & MongoDB (and the AdMob bug that nearly broke me)

Rahul Shinde — Mon, 21 Sep 2026 14:49:42 GMT

I just shipped BingeMark, a free Android app that tracks movies, TV shows and anime in one place. Here's the stack and two bugs that ate a weekend each.

The stack

Frontend: React Native + Expo (SDK 54)
Backend: Python + FastAPI
Database: MongoDB Atlas
Hosting: Render
Data: TMDB API (titles, images), OMDb (IMDb ratings)
Extras: Google Sign-In, Google Drive backup (drive.file scope), AdMob for ads

One app for movies, TV and anime

Most trackers pick one lane. I wanted all three. The trick was treating everything as TMDB-shaped data, anime is just TV/movie entries under the hood, so one data model and one UI handle all three instead of three separate flows.

Bug 1: AdMob broke my release build

Adding react-native-google-mobile-ads blew up the Gradle build with compileReleaseKotlin FAILED. The cause: the newer ads SDK was compiled with Kotlin 2.3, but Expo SDK 54 uses Kotlin 2.1 - a metadata mismatch. Fix: pin the library to a version that ships an older play-services-ads compiled against Kotlin 2.1. Lesson: with Expo, your native deps have to match the Kotlin version Expo bundles.

Bug 2: a rewatch that wouldn't save

Logging a second rewatch threw a 500. It was a classic Python datetime trap, comparing a naive datetime (from Mongo) with an aware one (freshly created) inside a max(). Fix: a small helper that normalizes everything to UTC-aware before comparing.

Takeaways

Match native dependency versions to your Expo/Kotlin version before you debug for hours.
Always store and compare datetimes as timezone-aware.
Keep one clean data model even when the content types look different. It saves you everywhere later.