# 400 invalid_request_error: fix the request, do not retry it
A 400 means the format or content of your request is wrong. Anthropic also uses this code for two things that are not request bugs at all, so classify first.
## What to do
1. Read the error message. It names the field or parameter that is wrong. Fix that field and resend.
2. If the message begins "You have reached your specified API usage limits" (or "specified workspace API usage limits"), your own spend limit is the cause, not your request. Raise or remove the limit in Console under Settings, then Billing. The message says when access resumes.
3. Catch-all rule: this error type is also used for other 4xx codes not listed in the docs. If the message does not name a field, check the request shape against the endpoint reference anyway.
4. Retry policy: never blind-retry a 400. Same request, same 400, forever. Fix first.
## The trap
Treating every 400 as a code bug. A spend-limit 400 is a billing setting, and no amount of request surgery clears it. The reverse trap: a spend-limit 400 looks like a validation bug, so you burn an hour rewriting a request that was fine.
## Checklist
- Distinguish "your request is malformed" from "your spend limit stopped you" by reading the message first.
- Own spend limit hit: 400. Tier monthly spend cap hit: 429 with error code enforced_spend_limit_reached. Know which one you are looking at.