I’m not sure if this will work with the direct lightening to USB C cable. You may need to use a dongle/adapter to your iPad for this to work properly, such as this: https://www.apple.com/shop/product/MK0W2AM/A/lightning-to-usb-3-camera-adapter

What iPad app are you using on your iPad to send MIDI clock? Does the H90 show up as a MIDI device in the app when you use the lightening > USB C cable? If not, then you’ll probably need to use the adapter.

My iPad has a USB C connecter, and the direct USB C > USB C connection works with the H90. You can use Logic Pro or other applications to send MIDI clock this way.