I just checked these folders and contrib repositories for r4.2 are empty:
https://ftp.qubes-os.org/repo/contrib/yum/r4.2/current/host/fc37/rpm/
https://contrib.qubes-os.org/yum/r4.2/current/host/fc37/rpm/
Are the contrib packages moved to somewhere else?
p.s.: Archive.org wayback machine link to document and log the server status:
Index of /yum/r4.2/current/host/fc37/rpm/