So I got a MIDIFlex 4 usb interface, and I’m trying to send the midi tracks on cubasis to an external synth (volca nubass.) It seems to work when I plug it into logic, but I can’t figure out how to make it work on my ipad… can anyone help? I’m no expert with MIDI, so I’m not 100% sure what I’m doing. cheers! 
I would check to see if your synth has been recognized by Cubasis. Click on ‘Routing/MIDI Output’ in a midi track’s info box.