iPhone Rekordbox - XDJ-RX3 Connection

Hi,

Sorry if a duplicate of anything, but I have searched.
I cannot seem to connect my iPhone Rekordbox app to the RX3.
I have Wi-Fi off as the guide says and connecting through a USB hub.  The RX3 comes up with a software control option when the source button is pressed, but the iPhone says connect to Wi-Fi or LAN etc.

Am I right in thinking I should be able to control the iOS Rekordbox app with the RX3 if the iphone is connected via the USB-B socket on the back?  The next thing to try is a dedicated cable, but I am not buying one to find out it doesn't work.