Behringer X1204USB and Logic X

Hi. Hope someone can help me here, otherwise my mixer is broken....but it's not. I shall explain.

I have a Behringer X1204USB and am trying to hook it up with my MacBookPro & Logic X. I have done this before and got it working but I tried yesterday and there was no audio signal reaching Logic X. There is a signal coming from the mac because I can here YouTube, iTunes, etc through the mixer and out my monitor speakers, but when I play my keyboard and synth there is nothing. I have selected USB audio Codec In/Out in the Audio MIDI setup app, I have selected USB audio Codec as In/Out sources via Network Preferences>>Sound and I have also told Logic X to use USB audio Codec In/Out on the Audio Preferences setup page. But when I play the instruments there is no audio, no bouncing green bars...no signal. So I am stuck now, is there another setting somewhere? There is one thing, on the Audio MIDI setup on the USB Audio Codec, the output has adjustable blue Master volume control, whereas the Input controls are greyed out, set to 0 and not adjustable.

Like I said audio from my Mac is present, through the mixer, so I have the mixer setup correctly. Also I have watched/read many helpful videos and threads and followed all instructions. I have also tried creating an aggregate device from here;

https://www.sweetwater.com/sweetcare/articles/how-do-i-make-an-aggregate-device-on-mac-os-x/

However not sure I got this right with reference to Clock source because obviously I'm just setting this up in my bedroom, not a professional studio where all sources need timing, Word Clock etc. Is it possible High Sierra is not compatible with this mixer. I'm pretty sure I upgraded to High Sierra since I last hooked up my mini studio but can't find anything about that here, or online. But then how come I can hear other audio from my Mac, just not my instruments in Logic X. So not even sure where the issue lies, is it Logic, is it the mixer, or the OS? Any suggestions would be gratefully received. Thanks