how to use Casio Privia PX850 as midi controller with GarageBand IOS

The Casio piano is working correctly as a MIDI controller with GarageBand MacOS on my MacMini, so I know that it's possible. But now I'd like to connect it to GarageBand on IOS.

MacOS setup, works fine with GarageBand MacOS:

piano => [ USB-B -- USB-A cable ] => [ 4-port usb hub] => [ USB-A -- USB-A cable ] => MacMini

IOS setup, no response in GarageBand IOS:

piano => [ USB-B -- USB-A cable ] => [ 4-port usb-C hub with USB-C tail ] => Ipad Air 4

piano => [ USB-B -- USB-A cable ] => [ 4-port usb hub] => [ USB-A -- lightning cable ] => iPhone X

Every device is updated to the latest version. IOS 14.5.1

Any suggestions? Are there any settings I need to look at? I see a Bluetooth MIDI setting in GarageBand, but nothing else. Do I need some kind of "Audio Unit Extension"?