ob-lilypond.el doesn't generate midi files

[Michael Maurer]

I've installed lilypond and customized ob-lilypond to use the
appropriate helper programs, but although it generates & shows pdfs
just fine, generating a midi file it does not. I execute tangle
on the codeblock, and all I get is "No midi file generated so can't play!".
org-version 9.4.6
emacs 27.2
Win 10