For Android:

This behavior may be omitted following migration guide: https://flutter.dev/docs/release/breaking-changes/network-policy-ios-android.

or... Just add in android/app/src/main/AndroidManifest.xml:

android:usesCleartextTraffic="true" to <application /> also dont forget to take INTERNET PERMISSION:

<uses-permission android:name="android.permission.INTERNET" /> <!-- This Line -->

<application
        android:name="io.flutter.app.FlutterApplication"
        android:label="receipt"
        android:usesCleartextTraffic="true" <!-- This Line -->
        android:icon="@mipmap/ic_launcher">

For iOS:

Allow insecure/HTTP requests globally across your application on iOS, you can add this to your ios/Runner/info.plist under the main dictionary definition:

<key>NSAppTransportSecurity</key>
<dict>
        <key>NSAllowsArbitraryLoads</key>
        <true/>
</dict>

Be warned that you will need to have an explanation for Apple's review team when enabling this, otherwise your app will get rejected on submission.

Thank you.

1. Navigate to your project.
2. Go to yourapp\android\app\src\debug\AndroidManifest.xml.
3. Add this line.

<application android:usesCleartextTraffic="true">
</application>

For further details, follow this link.

This problem is solved here.

https://flutter.dev/docs/release/breaking-changes/network-policy-ios-android

You just need to change the HTTP to HTTPS. Like this

Response response = await get('https://worldtimeapi.org/api/timezone/Africa/Nairobi');