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Unexpected status 503 Service Unavailable Codex

Quick fix

Configure v2ray or other proxy tools to bypass LAN traffic, resolving the 503 error when Codex accesses cc-switch local routing.

Symptom

Section titled “Symptom”
Error output
Unexpected status 503 Service Unavailable: Unknown error, url: http://127.0.0.1:15721/v1/responses

Cause

Section titled “Cause”

When using cc-switch to enable local routing for Codex, if system proxy tools like v2ray are enabled, they may intercept local requests to 127.0.0.1, causing Codex to fail connecting to the local service and report a 503 Service Unavailable error. Additionally, some users encountered variant errors when using NVIDIA NIM interfaces: because the upstream interface does not support the /v1/responses path, cc-switch receives a 404 Not Found error from the upstream when forwarding requests.

Fix

Section titled “Fix”

  1. Open the routing settings of v2ray or other proxy tools, add rules to bypass LAN (LAN) and mainland China domains, ensuring that local requests to 127.0.0.1 are not intercepted by the proxy.

Affected Versions

Section titled “Affected Versions”
ToolCodex
Version0.136.0
PlatformsmacOSWindows

Source Issues

Section titled “Source Issues”

This page is distilled from 2 real issues

FAQ

Section titled “FAQ”
Why does the 503 error disappear after disabling the proxy, but curl tests fail?
Because accessing external APIs requires a proxy. Directly disabling the proxy causes external requests to fail. The correct approach is to keep the proxy enabled but configure it to bypass the LAN (127.0.0.1), allowing local traffic to connect directly while external traffic goes through the proxy.
What causes the 404 Not Found error when using NVIDIA NIM?
This occurs because upstream providers like NVIDIA do not support the /v1/responses endpoint called by Codex. cc-switch receives a 404 error from the upstream when forwarding requests, which is an API compatibility issue.
Section titled “Related problems”
auth.json refilled with an existing account's auth.json - CodexUpgrade to v3.17.0+ and turn off 非接管切换时保留官方登录 (keep official login on non-takeover switch). Back up auth.json before upgrading.22 issues mergedcodex deepseek cannot select a model - cc-switchCodex desktop hides third-party models with no official ChatGPT login. Sign in once, enable keeping the official login in cc-switch, and restart Codex.5 issues mergedOnly a 200K context window shows in actual use - Claude CodeChange the default model in `~/.claude/settings.json` to the `[1m]` variant, or run `/model claude-opus-4-8[1m]` in the session, to activate the 1M context.5 issues merged

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