Why am I seeing net::ERR_CLEARTEXT_NOT_PERMITTED errors after upgrading to Cordova Android 8?

The default API level in the Cordova Android platform has been upgraded. On an Android 9 device, clear text communication is now disabled by default.

To allow clear text communication again, set the android:usesCleartextTraffic on your application tag to true:

<platform name="android">
  <edit-config file="app/src/main/AndroidManifest.xml" mode="merge" target="/manifest/application">
      <application android:usesCleartextTraffic="true" />
  </edit-config>
</platform>

As noted in the comments, if you have not defined the android XML namespace previously, you will receive an error: unbound prefix during build. This indicates that you need to add it to your widget tag in the same config.xml, like so:

<widget id="you-app-id" version="1.2.3"
xmlns="http://www.w3.org/ns/widgets" 
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:cdv="http://cordova.apache.org/ns/1.0">

There are two things to correct in config.xml So the right answer should be adding the xmls:android:

<widget id="com.my.awesomeapp" version="1.0.0" 
xmlns="http://www.w3.org/ns/widgets"
xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:cdv="http://cordova.apache.org/ns/1.0">

plus editing the config to allow:

<platform name="android">
  <edit-config file="app/src/main/AndroidManifest.xml" mode="merge" target="/manifest/application">
      <application android:usesCleartextTraffic="true" />
  </edit-config>
</platform>

If step 1 is avoided error: unbound prefix. will appear

Cleartext here represents unencrypted information. Since Android 9, it is recommended that apps should call HTTPS APIs to make sure there is no eves dropping.

However, if we still need to call HTTP APIs, we can do following:

Platform: Ionic 4

Create a file named: network_security_config.xml under project-root/resources/android/xml

Add following lines:

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
   <domain-config cleartextTrafficPermitted="true">
     <domain>ip-or-domain-name</domain>
   </domain-config>
</network-security-config>

Now in project-root/config.xml, update following lines:

<platform name="android">
    <edit-config file="app/src/main/AndroidManifest.xml" mode="merge" target="/manifest/application" xmlns:android="http://schemas.android.com/apk/res/android">
        <application android:usesCleartextTraffic="true" />
        <application android:networkSecurityConfig="@xml/network_security_config" />
    </edit-config>
    ... other statements...

It should work now.