fixed by comment https://github.com/fluttercommunity/flutter_webview_plugin/pull/523

android/src/main/AndroidManifest.xml

@@ -1,6 +1,7 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
           xmlns:tools="http://schemas.android.com/tools"
           package="com.flutter_webview_plugin">
+    <uses-sdk android:minSdkVersion="16" />
 
     <application>
         <provider

example/lib/main.dart

@@ -7,7 +7,7 @@ import 'package:flutter_webview_plugin/flutter_webview_plugin.dart';
 const kAndroidUserAgent =
     'Mozilla/5.0 (Linux; Android 6.0; Nexus 5 Build/MRA58N) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.94 Mobile Safari/537.36';
 
-String selectedUrl = 'https://damp-coast-35782.herokuapp.com';
+String selectedUrl = 'https://flutter.io';
 
 // ignore: prefer_collection_literals
 final Set<JavascriptChannel> jsChannels = [