Newbie here, sorry if this is an obvious fix.
I just installed MagicMirror on a Pi 3 A+ yesterday. I can start the magic mirror application but it only displays a blank black screen.
I followed the following installation guide: https://docs.magicmirror.builders/getting-started/installation.html#manual-installation

full error message:
“unable to write js/positions.js with the discovered module positions make the MagicMirror/js folder writeable by the uder starting MagicMirror”

I’ve attempted to change ownership of the folder but was unsuccessful.