Dev Builds & Metro

React Native and Expo apps built in development mode do not embed their JavaScript bundle. Instead, they load it at runtime from a Metro dev server running on your machine. TesterArmy test devices run in the cloud and cannot reach your local Metro server, so a dev-mode app cannot start.

How this failure looks

When a dev-mode build is uploaded, the app launches but immediately shows one of these screens instead of your app:

A red error screen with “No script URL provided”
“Could not connect to development server”
“Unable to load script. Make sure you’re either running Metro…”
The Expo dev launcher asking for a development server URL

When the agent detects this, the run fails with the step error code MOBILE_RELEASE_BUILD_REQUIRED and links to this page.

Why it happens

Development builds (Debug configuration on iOS, debug variant on Android, and Expo builds with expo-dev-client / developmentClient: true) expect a Metro dev server to serve the JavaScript bundle over the network. That works on your machine and simulator, but not on a remote test device. TesterArmy needs a self-contained build with the JavaScript bundle embedded in the app binary.

How to fix it

Build a release artifact and upload that instead.

iOS
Android

Build a Release iOS Simulator app. For Expo / React Native projects, generate native files first if needed:

npx expo prebuild --platform ios

xcodebuild -workspace ios/MyApp.xcworkspace \
  -scheme MyApp \
  -configuration Release \
  -sdk iphonesimulator \
  -destination 'generic/platform=iOS Simulator' \
  -derivedDataPath ios/build \
  build

The -configuration Release flag is what embeds the JavaScript bundle. The simulator app bundle ends up under:

ios/build/Build/Products/Release-iphonesimulator/MyApp.app

Build a release APK:

npx expo prebuild --platform android

cd android
./gradlew assembleRelease

Debug APKs usually require MetroBy default, React Native only bundles JavaScript into release variants. A ./gradlew assembleDebug APK works only if your build embeds the bundle for debug builds too. When in doubt, upload the release APK.

Release builds must be signed. If you have not configured a release keystore, the default Expo prebuild setup signs release builds with the debug keystore, which is fine for testing.

Expo EAS builds

If you build with EAS, make sure the build profile you upload from does not use a development client:

{
  "build": {
    "testerarmy-ios-simulator": {
      "ios": { "simulator": true }
    },
    "testerarmy-android-apk": {
      "android": { "buildType": "apk" }
    }
  }
}

Avoid "developmentClient": true in the profile used for TesterArmy uploads - it produces an expo-dev-client build that opens the dev launcher instead of your app. See Expo EAS for the full CI workflow.

Verify before uploading

To check a build locally, install it on a simulator/emulator without Metro running (do not run npx expo start or npm start) and launch it. If the app opens normally, it is self-contained and ready to upload. See App Uploads for upload instructions.

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Resources

How this failure looks

Why it happens

How to fix it

Expo EAS builds

Verify before uploading

​How this failure looks

​Why it happens

​How to fix it

​Expo EAS builds

​Verify before uploading

How this failure looks

Why it happens

How to fix it

Expo EAS builds

Verify before uploading