What 401 / 402 / 404 / 429 / 5xx mean and what to check first.
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.
Lower your concurrency or retry shortly. Contact us if you need a higher limit.
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.