I am running iOS 12.1.2 on my iPhone X. I am trying to use GarageBand with a Microkorg synthesizer, and am connecting them using a Roland UM-One Mk2 MIDI interface and a USB 3 Lightning Camera Adapter.
This setup seems to work fine on my iPad - also running the most recent version of iOS 12.
But when I plug everything into my iPhone, I cannot play the GarageBand instrument with the synth.
Also, the expected lights on the MIDI interface are on in both cases.
Is there a setting on the iPhone that must be changed? I literally just had to plug in to the iPad to make it work - no extra effort there.