Cubasis Hardware Synth Routing

i can‘t get a damn signal out of my steinberg ur rt4 interface in cubasis on the ipad pro . I want to record my sub 37 synth . In the setups i see the interface . I make a audio track and take the correct channel and put the volume on . But i just can‘t get a signal it doesn‘t work . Please can anyone help me ??? .

According to Steinberg your audio-interface is class compliant and should work with the camera conncection kit or with an USB to Lightening adapter.

This said, it should be one of the connections or a mismatch of a channel.