First option
Set Internet Access to Require in the project settings
Second Option
Create path Asset/Plugins/Android, and place the custom AndroidManifest.xml file in it (granting internet access )
<manifest
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">
<uses-permission android:name="android.permission.INTERNET" />
<application>
<activity android:name="com.unity3d.player.UnityPlayerActivity"
android:theme="@style/UnityThemeSelector">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
<meta-data android:name="unityplayer.UnityActivity" android:value="true" />
</activity>
</application>
</manifest>