I manage to deploy an app with a download function to create a pdf document. I looked around at different ways of altering the font etc and came up with the following YAML.
I believe xelatex is using system fonts (i.e. fonts on your local machine), so is it possible that wherever you are deploying the app does not have the same fonts?
Yes, I believe that is what is being suggested in the other thread. Include the font file in the app bundle and refer to it with a relative path from the root dir.