As Ben suggests, you can contact Apple and request a refund; refunds are given at Apple’s discretion, and there is nothing that an app developer can do to handle a refund for an app or in-app purchase bought from the App Store.
Apple’s App Store support representative may well ask you to contact the app developer in the first instance before they provide you with a refund, and you can send them a link to this thread as evidence that you have contacted us, and indeed point them specifically to this reply, since I am a Steinberg representative.
Obviously I’m sorry to hear that you find Dorico for iPad unsuitable for your use. Because Dorico is built using the cross-platform Qt framework, it requires considerable effort for us to add support for iOS-level hardware and software features that are not already supported by Qt. Although Qt’s support for iOS is really pretty good, unfortunately it tends to lag behind the latest software and hardware features added by Apple, and at the present time, Qt does not support the Magic Trackpad on iOS.
It is possible for us to add support for these things ourselves, of course, but this is a non-trivial effort that requires careful prioritisation within our small development team. As you will understand from your own working life, there is an opportunity cost associated with everything you decide to work on: when you are working on something, you cannot work on anything else.
We are planning to move up to the latest version of Qt in our next major development cycle, which should provide benefits across all of our targeted platforms, though so far as I know even the most recent version of Qt still does not provide support for the Magic Trackpad.
We understand that this is an issue that is important to you, and one way or another we do plan to support scrolling via the trackpad in a future release, but unfortunately I cannot provide a timescale for when this is likely to happen.
In the meantime, a new update of Dorico for iPad will be released soon, alongside the next update to Dorico for macOS and Windows, which will bring a number of improvements in keyboard handling and will fix issues experienced by some users on specific iPad models with the app freezing when you attempt to interact with certain UI elements, along with a good number of improvements shared with Dorico for macOS and Windows.
I hope that you will keep an eye on Dorico for iPad and be willing to give it another try in future.