I’m trying to communicate from native android app with smart card via external usb card reader.

This detects card reader properly and permission is fine.

fun scanUsbDevices(usbManager: UsbManager) {
    this.usbManager = usbManager

    devices.clear()
    for (device in usbManager.deviceList.values) {
        var h_d: UsbEndpoint? = null
        var d_h: UsbEndpoint? = null

        for (i in 0 until device.interfaceCount) {
            val usbInterface = device.getInterface(i)
            for (j in 0 until usbInterface.endpointCount) {
                val ep: UsbEndpoint = usbInterface.getEndpoint(j)

                if (ep.type == UsbConstants.USB_ENDPOINT_XFER_BULK) {
                    if (ep.direction == UsbConstants.USB_DIR_OUT) {
                        // from host to device
                        h_d = ep

                        if (d_h != null) {
                            devices.add(DataUsbDevice(device, h_d, d_h, usbInterface))
                            return      // should not return here, but break
                        }
                    } else if (ep.direction == UsbConstants.USB_DIR_IN) {
                        // from device to host
                        d_h = ep

                        if (h_d != null) {
                            devices.add(DataUsbDevice(device, h_d, d_h, usbInterface))
                            return      // should not return here, but break
                        }
                    }
                }
            }
        }
    }
}

Function to send APDU command and receive response

fun writeToSelected(command: ByteArray): String {
    val connection: UsbDeviceConnection? = usbManager?.openDevice(devices[cur_device_id].device)

    if (connection != null) {
        val claimed: Boolean = connection.claimInterface(devices[cur_device_id].usb_interface, true)

        if (claimed) {
            // tried bulk transfer here from host to device, didn't work
            val transferred = connection.controlTransfer(
                UsbConstants.USB_TYPE_VENDOR, 0x01, 0, 0, command, command.size, 3000
            )

            // tried adding delay here

            if (transferred >= 0) {
                // Read response from the smart card reader
                val buffer = ByteArray(devices[cur_device_id].device_to_host_ep.maxPacketSize)
                val readBytes = connection.bulkTransfer(
                    devices[cur_device_id].device_to_host_ep, buffer, 0, buffer.size, 3000
                )
                if (readBytes >= 0) {
                    return buffer.copyOf(readBytes).toString(Charsets.UTF_8)
                } else
                    "err 2"

            } else {
                return "ERR 3"
            }
        }
    } else {
        return "conn is null"
    }

    return "OTHER ERROR"
}

// Example APDU command 
val apduCommand = byteArrayOf(
    0x00,          // CLA (Class)
    0xA4.toByte(), // INS (Instruction)
    0x04,          // P1 (Parameter 1)
    0x00,          // P2 (Parameter 2)
    0x10,          // LC (Data Length)
    0xA0.toByte(), 0x00, 0x00, 0x07, 0x48, 0x46, 0x4A, 0x49, 0x2D, 0x54, 0x61, 0x78, 0x43, 0x6F, 0x72, 0x65, // Command Data
    0x00           // Le (Expected Length)
)

Same APDU command works fine on windows with pcsc-sharp c#.
card readers also return different outputs.

I expect it to return 0x9000.

Is this even possible on android phone or am i doing something wrong?

Is it because usb-otg port?

Is UsbManager too low level and requires something to be build on top of it?