USB Device not found

[A Former User]

Hi

I am new to Qt and Android development so please be kind.

I am trying to talk to a USB device using Qt and LibUsb-1.0.23.

I have set up the AndroidManifest as follows and the USB device is detected and the application automatically opened upon connecting the USB device so all good.
I also have 'Serial USB Terminal' installed which can see the device has the correct VID and PID as defined in the device_filter.xml.

However the call to libusb_get_device_list always returns 0.

Is there some other android access/permission setting I am missing?
Any help greatly appreciated as I have spent a lot of time on this. TIA

<?xml version="1.0"?>
<manifest package="org.qtproject.example" xmlns:android="http://schemas.android.com/apk/res/android" android:versionName="-- %%INSERT_VERSION_NAME%% --" android:versionCode="-- %%INSERT_VERSION_CODE%% --" android:installLocation="auto">
<!-- The following comment will be replaced upon deployment with default permissions based on the dependencies of the application.
Remove the comment if you do not require these default permissions. -->
<!-- %%INSERT_PERMISSIONS -->
<uses-permission android:name="android.permission.USB_PERMISSION"/>
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

<!-- The following comment will be replaced upon deployment with default features based on the dependencies of the application.
     Remove the comment if you do not require these default features. -->
<!-- %%INSERT_FEATURES -->
<uses-feature android:name="android.hardware.usb.host"/>

<supports-screens android:largeScreens="true" android:normalScreens="true" android:anyDensity="true" android:smallScreens="true"/>
<application android:hardwareAccelerated="true" android:name="org.qtproject.qt5.android.bindings.QtApplication" android:label="-- %%INSERT_APP_NAME%% --" android:extractNativeLibs="true">
    <activity android:configChanges="orientation|uiMode|screenLayout|screenSize|smallestScreenSize|layoutDirection|locale|fontScale|keyboard|keyboardHidden|navigation|mcc|mnc|density" android:name="org.qtproject.qt5.android.bindings.QtActivity" android:label="-- %%INSERT_APP_NAME%% --" android:screenOrientation="unspecified" android:launchMode="singleTop">
        <intent-filter>
            <action android:name="android.intent.action.MAIN"/>
            <category android:name="android.intent.category.LAUNCHER"/>
            <action android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED"/>
        </intent-filter>
        <!-- Application arguments -->
        <!-- meta-data android:name="android.app.arguments" android:value="arg1 arg2 arg3"/ -->
        <!-- Application arguments -->
        <meta-data android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" android:resource="@xml/device_filter"/>
        <meta-data android:name="android.app.lib_name" android:value="-- %%INSERT_APP_LIB_NAME%% --"/>

Calling code from Qt
// get list of usb
libusb_context* context;
int result = libusb_init (&context);
if (result < 0)
{
restartOk = false;
qDebug() <<"UNABLE_INITAILIZE_LIBUSB";
}

ssize_t cnt; // holding number of devices in list
libusb_device **list_of_devices;
cnt = libusb_get_device_list(context, &list_of_devices);