Não é permitida a conexão com o servidor

D/NetworkSecurityConfig: No Network Security Config specified, using platform default
W/System.err: java.io.IOException: Cleartext HTTP traffic to 172.18.245.236 not permitted
W/System.err:     at com.android.okhttp.HttpHandler$CleartextURLFilter.checkURLPermitted(HttpHandler.java:115)
W/System.err:     at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:458)
        at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:127)
        at com.android.okhttp.internal.huc.HttpURLConnectionImpl.getOutputStream(HttpURLConnectionImpl.java:258)
W/System.err:     at com.fulltime.agenda.web.WebClient.enviaJsonParaOEndereco(WebClient.java:29)
W/System.err:     at com.fulltime.agenda.web.WebClient.insereAluno(WebClient.java:19)
        at com.fulltime.agenda.web.task.InsereAlunoTask.doInBackground(InsereAlunoTask.java:23)
W/System.err:     at android.os.AsyncTask$2.call(AsyncTask.java:333)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
        at java.lang.Thread.run(Thread.java:764)

Eu estava tendo este problema, consegui arrumar acrescentando a seguinte linha no arquivo AndroidManifest.xml

<manifest ...>
    <uses-permission android:name="android.permission.INTERNET" />
    <application
        ...
        android:usesCleartextTraffic="true"
        ...>
        ...
    </application>
</manifest>

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