When connecting to a Raspberry PI using the RDP protocol, please make sure you're running the latest version of XRDP as older versions of XRDP (0.9.1 or earlier) that ship with the PI have know bugs that prevent it from working with Jump Desktop's RDP engine.
Here's how you can update the XRDP distribution of on PI. In the Terminal type these in:
echo 'deb http://httpredir.debian.org/debian stretch-backports main contrib non-free' | sudo tee -a /etc/apt/sources.list.d/debian-backports.list sudo apt-get update sudo apt-get -t stretch-backports install xrdp sudo service xrdp restart
Much thanks to user Ketan Kothari for providing these steps!