You iPad needs to be of more recent vintage. Many of us Roon users who were waiting for the remote iPad app found out at the app's launch that our units weren't compatible.
Here's a link to the thread at Roon. Somewhere is there is a listing of the iPad units that will work with Roon.
https://community.roonlabs.com/t/feedback-on-ios-hardware-requrements/3227/54
Some of us were more upset than others but Roon has handled the complaints with their usual professionalism.
I have had great success using the Real VNC app to remote control the Mac Mini I use to run iTunes/Tidal/Roon. So I have a workaround until I upgrade my iPad. I've seen it run on my GF's iPad and it is terrific.