radtel rt-900 firmware update over bluetoothapp failed? Anyone else?

Just bought a new Radtel RT-900. Of course, I am aware this is not the top handheld, but I was just curious and snooping around in the amateur radio hobby. The problem I am having is that the Radtel app provides an option to update the radio over Bluetooth, yet after connecting to "walkie-talkie" in the first window, the second window with the .rar package shows that the device status is "disconnected". Are there any solutions? Or should I just buy a programming cable?