What 401 / 402 / 404 / 429 / 5xx mean and what to check first.
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The token is wrong, deleted, or malformed. Check the header reads
Bearer sk-xxx — note the space after Bearer.
Not enough balance for this request's hold. Top up and it resumes; no config change needed.
Almost always a wrong URL. Confirm you use https://api.router.ai/v1/... with exactly one
/v1. A misspelled model name also returns 404 — model ids are listed on the Models page.
An upstream rate limit was hit. Just retry.
The upstream model service failed. We pass through the original upstream error body so you can diagnose it. These are usually transient — retry. Tell us if one model fails persistently.
Suggested order: status code → message in the body → your billing log. If the call is absent from your billing log, it never reached us and the problem is client-side.