Newbie : Headphone monitoring DDJ 200 , iPhone, WeDJ.

Hi Guys, Humour me : I have searched the forum and explored as many resources as I could find and still cant solve the following - 

I just can't get the signal to split for headphone monitoring, Master output only to phones and speakers no matter what channel button selection is made.

The following have been checked:

App audio settings and levels.

iPhone (8) Lighting Output to headphone jack (Ok) ... (I'm getting sound!) 

Supplied Splitter Cable : As above

Controller and App Headphone button selection light up accordingly.

Cross checked with various headphones and speaker sets combinations.

I cant find any additional audio output controls in the iPhone menus,

Any thoughts welcome... Cheers.

Steve C . UK 'Learning in Lock-down'