I'm trying to install a Postgres extension (h3) with pgxn. I have three versions of Postgres installed on my machine via Postgres.app: 15, 16, and 17. I would like to install h3 in the 15 database. The command I used was:

pgxn install --pg_config /Applications/Postgres.app/Contents/Versions/15/bin/pg_config h3

When the install command is running, I see that it's installing into the 17 database instead. Here's an line from the logs that seems telling:

-- Found PostgreSQL: /Applications/Postgres.app/Contents/Versions/17/lib/libpq.dylib (found version "17.1")  missing components: PostGIS

I've triple-checked that the path I specified for --pg_config exists. Does anyone know why pgxn might be picking up the wrong version, or how else I can troubleshoot this?