No Audio Signal Vestax Vci 400DJ iPad

Hi! I use a Vestax Vci 400 DJ (Silver Serato Edition) but I would love to change to iPad or iPhone instead of my MacBook. When I connect the Controller with the iPad, every midi signals are working fine, but I have no audio output neither headphone nor master. VU- Meter is flashing so there must be a signal somewhere, right?

I tried changing all the audio settings but no result. With the macOS app I don’t have audio issues.

Any recommendations what I can do to fix the problem?