@ValentineHerr thank you so much- tested and working.
Usability issue: Note that output profiles must be up to date- if the app adds extra variables and an older output profile is selected (missing the newer entities), the download won't work. I think this is not a problem whilst we are testing the app but making a note incase it's something we need to explain in the user support documents in order to futureproof the app.
from @Geopicka here