RUN echo -n "\n[custom]" >> /var/www/html/apps.txt
did you copy paste this?
Did you change “[custom]” to name of your app?
These are example images made from 5 community apps, it has POSAwesome which does all the magic with Vue built static assets. It acts as example to showcase how JS building apps can be packaged. It works. If you fork it and make relevant changes there you’ll have better success.