Add permission to android/app/src/main/AndroidManifest.xml:

<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.REQUEST_INSTALL_PACKAGES" />

Make sure you have a release keystore (key.jks or .keystore). If you do not have one, create it: If you want the keystore to live in the project (convenient for local builds), create it in the android folder of your repo: Run this command from the root of your project

# from project root (PowerShell) creates for 10000 days validity
keytool -genkey -v -keystore ".\android\release-key.jks" -alias release_key -keyalg RSA -keysize 2048 -validity 10000

Add key.properties in android/ with your keystore details:

storePassword=<your-store-password>
keyPassword=<your-key-password>
keyAlias=release_key
storeFile=android/release-key.jks

Add to .gitignore

/key.properties
/android/release-key.jks

Configure build.gradle (not done currently)

Build the signed APK

flutter clean
flutter pub get
flutter build apk --release
# output: build/app/outputs/flutter-apk/app-release.apk

Or build an AAB if you plan to upload to Play Store: flutter build appbundle --release

Compute SHA-256 of APK (for manifest)

Get-FileHash .\build\app\outputs\flutter-apk\app-release.apk -Algorithm SHA256

manifest.json

{
  "versionName": "1.0.0",
  "versionCode": 1,
  "notes": "Initial public release",
  "apk_url": "https://github.com/Subhranil2004/instruo-app/releases/download/v1.0.0/app-release.apk",
  "sha256": "PASTE_SHA256_HEX_HERE"

}