Have tried various methods of sequencing P4, Controller, IPad Air 2 (WiFi only) with DJI GO 4 app, not able to connect to P4.  Latest firmware, latest IOS 11.2.1, tried several cords.  Have IPhone 6S PLUS connecting fine, IPad Pro 12.9 (WiFi only) connecting fine.  Posted on old thread, apologize if this is duplicate.  Have cleaned and restarted new as well.  Like to have Air 2, as dedicated primary on flights.  Thoughts?

What's the current version of  DJI GO 4? Could you post a screenshot of the About page of iPad? Alternatively, you can connect with iTunes to refresh the OS.

. Thanks for quick response.  Did sync to iTunes a little while ago.  

Got it resolved.  Haven’t restored from ITunes in a long time.  
Connected and flying.  Thanks, again.