spotifyd OAuth crashes

This is current/arm64, with spotifyd-0.4.1.
The pkg readme says

Authentication via OAuth must be set up using

$ spotifyd authenticate -c .

This will redirect you to a web browser to complete the OAuth process,
then place a credentials.json file in the current directory.

Running "spotifyd authenticate -c ." says

[INFO] Loading config from "/etc/spotifyd.conf"
[INFO] Failed reading config file: Permission denied (os error 13)
Browse to: https://accounts.spotify.com/authorize?response_type=code&client_id=65b708073fc0480ea92a077233ca87bd&state=ViKP4gn23HzjcohoC8SMqg&code_challenge=1tikZyQSlpaDrvJL0D81fZ2hi36iKOXam7MbBW3QBw4&code_challenge_method=S256&redirect_uri=http%3A%2F%2F127.0.0.1%3A8000%2Flogin&scope=app-remote-control+playlist-modify+playlist-modify-private+playlist-modify-public+playlist-read+playlist-read-collaborative+playlist-read-private+streaming+ugc-image-upload+user-follow-modify+user-follow-read+user-library-modify+user-library-read+user-modify+user-modify-playback-state+user-modify-private+user-personalized+user-read-birthdate+user-read-currently-playing+user-read-email+user-read-play-history+user-read-playback-position+user-read-playback-state+user-read-private+user-read-recently-played+user-top-read
[INFO] OAuth server listening on 127.0.0.1:8000

and when I point my browser to 127.0.0.1:8000,
the page merely says

"Go back to your terminal :)"

where I am told

Error:
0: token retrieval failed
1: Auth code param not found in URI http://localhost

Location:
src/oauth.rs:63


Am I missing something obvious?

It also says

Backtrace omitted. Run with RUST_BACKTRACE=1 environment variable
to display it. Run with RUST_BACKTRACE=full to include
source snippets.


but either of those just say "empty backtrace".

Jan