Check out this link:
https://www.itg.ias.edu/remoteapp-ios-setup
Something to note - I am fairly confident that you will get certificate errors if you use a self-signed certificate for the https connection. And if the website is not outside facing (ie accessible from the web), you will need to make sure your ipad is connected to the same network as the computer (may require VPN) and has access to the computer for it to work.
Unfortunately, I have no ipad or any apple devices, but I was able to make this work on an android device using a certificate signed from the our corporate CA, which got added as a trusted root CA when I added my exchange account to my device.
If you are unable to get the RAWeb feed working, chances are you also cannot access the RAWeb feed from the website in your browser either or you are getting a warning while connecting.
That being said, if you have windows server 2012 R2, is there a reason you are not using the built-in tools for remoteapps rather than using the RemoteApp Tool?