@miiindbullets Ah okay. No, the camera adapter just has a lightning power inlet next to the "camera" inlet.

I wonder if there's some kind of workaround...

Seems to defeat the whole purpose of having the Pianoteq app on your phone to use as a sound module if the sounds are just coming out of the tiny phone speakers.

Would something like this work (using the lightning-out on the camera adapter)?--converts lightning to balanced 1/4in male
https://www.amazon.com/dp/B0895WTVGZ/

I'm pretty sure that will not work--that the lightning port coming out of the camera adapter is only for power (so you can charge your phone with the normal charging cable while using the adapter) and does not work as an extra data connector.

What I and probably most people who are using an iOS device do, is use a USB hub (like I mentioned before) and plug an audio interface into that, which will then output to headphones or speakers. A low-latency audio interface (like any of the focusrite scarlett line) is a great enhancement to the sound and gives you separate volume controls for speakers and headphones. And it can also be used for other purposes (microphone input, say). Yes, it is a lot of cables, not as clean and simple as I would like, but works very well as an alternative to a laptop. I like the UI on the iOS version of Pianoteq, with touch capabilities, better than on the laptop.

https://www.amazon.com/Adapter-Headphon...B07P94PB7Z

That would let you send MIDI over USB from the controller to the iPhone, and audio out from the phone to your headphones or speakers. The adapter you're using today would work if your keyboard had an integrated audio interface (most of the newer Yamaha, Roland, and StudioLogic digital/stage pianos have them). There may be other ways to make it work, but I used the above adapter. Hope that helps!

I wonder if there's some kind of workaround...

Seems to defeat the whole purpose of having the Pianoteq app on your phone to use as a sound module if the sounds are just coming out of the tiny phone speakers.

Would something like this work (using the lightning-out on the camera adapter)?--converts lightning to balanced 1/4in male
https://www.amazon.com/dp/B0895WTVGZ/

How can I use my casio cdp-s350 as a controller and get the sounds from Pianoteq Stage 8 on an iPhone XS?
I'm using a lightning cable from the iPhone to an adapter, which changes usb-a to usb-b.
This is plugged into the keyboard.
But I'm unable to hear the Pianoteq sounds.

Is Pianoteq noticing the keyboard--are you able to select it and does pressing the keyboard keys reflect in the UI?
Is the keyboard powered separately, or does it rely on the phone for power? If the latter, then the iPhone likely does not provide sufficient power for the keyboard.
You will need to connect the phone to a powered USB hub (using the same adapter), plug the USB hub into power, and then plug your keyboard USB into the hub.