Where is `processing-java` looking for libraries?

When I’m running processing on a headless server as described at https://github.com/processing/processing/wiki/Running-without-a-Display, where does it expect the libraries to be?

I’m running xvfb-run /opt/processing-3.5.3/processing-java --sketch=/srv/data/FTX/receiving_data/ --run & in a bash script but it is giving me

No library found for http.requests
Libraries must be installed in a folder named 'libraries' inside the sketchbook folder (see the Preferences window).
receiving_data.pde:0:0:0:0: The package “http” does not exist. You might be missing a library.

Instead of me copying putting the libraries where it is looking for them, it would be even better if I could tell it where they are. Is there an option for that?