you need nix with flakes enabled. this ensures the build is deterministic. then you can run everything with a single command:

nix run . -- \
  --playlist <spotify url> \
  --client-id <get this from api.spotify.com> \
  --client-secret <get this from api.spotify.com> \
  --username <soulseek username> \  # you can set these to literally anything...
  --password <soulseek password> \  # ...or just use the same as in soulseekqt
  --downloads <target folder> \
  --shared <share folder> \         # optional but peers often require that you share stuff
  --debug                           # optional

you can also build everything with nix build, but then you have to manually put slskd on the $PATH before executing the binary. not recommended.

you can also hack on it with nix develop. after that you might want cabal repl.