Hi Cat - the reason you’re seeing this error is because BEAST is graphical program (or at least opens a graphical window to select the .xml file for analysis). SSH-ing to your instance means that, by default, there isn’t a display connected to the terminal you’re working on, so there’s no display to send this window to, hence the error message.
You can make your instance forward graphics to your local display (i.e. your local monitor) by using the -X (forward X11) and -C (enable compression) flags when SSHing from the mac terminal:
This applies for every graphical program (ACT, Artemis, Beauti, Firefox, etc), but expect the graphics to be a bit clunky, because you’re having to move them across the Internet rather than the cable that connects your monitor directly to the computer.
Alternatively, you can skip the graphical bit altogether and just run: