Can you direct me to a page where I can buy such a cable? I have bought one on eBay, but with no luck in setting it up.

Currently I am trying to set up the xKey 37 Air via the Widi bud. The xKey Grand Piano app on my PC says “XKEY NOT CONNECTED” even though the PC app Widi Bud says “1 MIDI Device(s) nearby connected (not scanning)” and when I close that and open xKey Plus it says “Connection mode: Wireless bluetooth (Widibud) Activation status: Yes”, but I cannot get the xKey Air to connect to my xKey Grand Piano app. Why?

It only says “XKEY NOT CONNECTED” and all the time the blue light on the xKey is on, and the red light is flashing.