Spotify blocks API calls from server IPs (open.spotify.com/api/* times out, api.spotify.com/v1/ returns 429). Setting SPOTIFY_PROXY routes all Spotify calls through curl_cffi via that proxy, bypassing the IP ban. Without proxy, SpotipyFree is still tried (works on non-banned IPs). A clear tip is printed if SpotipyFree fails without a proxy configured. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>