Android 8: Cleartext HTTP traffic not permitted

https://stackoverflow.com/questions/45940861/android-8-cleartext-http-traffic-not-permitted 

Also have a look at Android M and the war on cleartext traffic

Codelabs explanation from Google

Option 1 -

First try hitting the URL with https:// instead of http://

Option 2 -

Create file res/xml/network_security_config.xml -

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <domain-config cleartextTrafficPermitted="true">
        <domain includeSubdomains="true">api.example.com(to be adjusted)</domain>
    </domain-config>
</network-security-config>

AndroidManifest.xml -

<?xml version="1.0" encoding="utf-8"?>
<manifest ...>
    <uses-permission android:name="android.permission.INTERNET" />
    <application
        ...
        android:networkSecurityConfig="@xml/network_security_config"
        ...>
        ...
    </application>
</manifest>

Option 3 -

android:usesCleartextTraffic Doc

AndroidManifest.xml -

<?xml version="1.0" encoding="utf-8"?>
<manifest ...>
    <uses-permission android:name="android.permission.INTERNET" />
    <application
        ...
        android:usesCleartextTraffic="true"
        ...>
        ...
    </application>
</manifest>

Also as @david.s' answer pointed out android:targetSandboxVersion can be a problem too -

According to Manifest Docs -

android:targetSandboxVersion

The target sandbox for this app to use. The higher the sandbox version number, the higher the level of security. Its default value is 1; you can also set it to 2. Setting this attribute to 2 switches the app to a different SELinux sandbox. The following restrictions apply to a level 2 sandbox:

• The default value of usesCleartextTraffic in the Network Security Config is false.
• Uid sharing is not permitted.

So Option 4 -

If you have android:targetSandboxVersion in <manifest> then reduce it to 1

AndroidManifest.xml -

<?xml version="1.0" encoding="utf-8"?>
<manifest android:targetSandboxVersion="1">
    <uses-permission android:name="android.permission.INTERNET" />
    ...
</manifest>

ERROR

Java.IO.IOException: Cleartext HTTP traffic to localhost not permitted
  at Java.Interop.JniEnvironment+InstanceMethods.CallVoidMethod (Java.Interop.JniObjectReference instance, Java.Interop.JniMethodInfo method, Java.Interop.JniArgumentValue* args) [0x00068] in /Users/runner/work/1/s/xamarin-android/external/Java.Interop/src/Java.Interop/Java.Interop/JniEnvironment.g.cs:11884 
  at Java.Interop.JniPeerMembers+JniInstanceMethods.InvokeAbstractVoidMethod (System.String encodedMember, Java.Interop.IJavaPeerable self, Java.Interop.JniArgumentValue* parameters) [0x0001a] in /Users/runner/work/1/s/xamarin-android/external/Java.Interop/src/Java.Interop/Java.Interop/JniPeerMembers.JniInstanceMethods_Invoke.cs:47 
  at Java.Net.HttpURLConnectionInvoker.Connect () [0x00000] in /Users/runner/work/1/s/xamarin-android/src/Mono.Android/obj/Release/monoandroid10/android-29/mcw/Java.Net.HttpURLConnection.cs:725 
  at Xamarin.Android.Net.AndroidClientHandler+<>c__DisplayClass44_0.<ConnectAsync>b__0 () [0x0007d] in /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Xamarin.Android.Net/AndroidClientHandler.Legacy.cs:356 
  at System.Threading.Tasks.Task.InnerInvoke () [0x0000f] in /Users/builder/jenkins/workspace/archive-mono/2020-02/android/release/external/corert/src/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs:2476 
  at System.Threading.Tasks.Task.Execute () [0x00000] in /Users/builder/jenkins/workspace/archive-mono/2020-02/android/release/external/corert/src/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs:2319 
--- End of stack trace from previous location where exception was thrown ---

  at Xamarin.Android.Net.AndroidClientHandler.DoProcessRequest (System.Net.Http.HttpRequestMessage request, Java.Net.URL javaUrl, Java.Net.HttpURLConnection httpConnection, System.Threading.CancellationToken cancellationToken, Xamarin.Android.Net.AndroidClientHandler+RequestRedirectionState redirectState) [0x000e4] in /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Xamarin.Android.Net/AndroidClientHandler.Legacy.cs:405 
  at Xamarin.Android.Net.AndroidClientHandler.SendAsync (System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) [0x00286] in /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Xamarin.Android.Net/AndroidClientHandler.Legacy.cs:287 
  at System.Net.Http.HttpClient.FinishSendAsyncBuffered (System.Threading.Tasks.Task`1[TResult] sendTask, System.Net.Http.HttpRequestMessage request, System.Threading.CancellationTokenSource cts, System.Boolean disposeCts) [0x0017e] in /Users/builder/jenkins/workspace/archive-mono/2020-02/android/release/external/corefx/src/System.Net.Http/src/System/Net/Http/HttpClient.cs:506 
  at ChecadorCamion.Clases.MyApi.Query (System.String Endpoint, System.Collections.Generic.List`1[T] ApiParametersList) [0x00115] in C:\Users\jgalvan\source\repos\ChecadorCamion\ChecadorCamion\ChecadorCamion\Clases\MyApi.cs:76 
  --- End of managed Java.IO.IOException stack trace ---
java.io.IOException: Cleartext HTTP traffic to localhost not permitted
	at com.android.okhttp.HttpHandler$CleartextURLFilter.checkURLPermitted(HttpHandler.java:127)
	at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:462)
	at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:131)
}