You must also install a suitable X Server. The preferred X server is available from the XQuartz Website You must also set up the MacPorts repository. Follow the instructions closely on the MacPorts website to configure the repository. Once MacPorts is configured, open a terminal and enter the following commands which will download, compile and install the required packages.
sudo port install perl5 p5-gtk3 p5-soap-lite freerdp
Unpack the RemoteBox tarball and change into the RemoteBox-x.y directory. Important. Newer versions of macOS don't seem to need this, but for older versions you may need to open the remotebox file in a text editor and replace:
Launch RemoteBox as follows: