Schema, contract, and parameter constraint validation failures.
Last reviewed: February 13, 2026|54 mapped errors|Page 4 of 4
Validation errors indicate request payload, query parameters, or API contract expectations were not satisfied by caller input.
Provider-specific error pages mapped to this category (54 total). Showing 46-54.
HTTP 405 Method Not Allowed means the resource exists but does not support the HTTP method used.
HTTP 406 Not Acceptable means the server cannot produce a representation matching proactive negotiation headers.
HTTP 411 Length Required means the server requires a defined Content-Length for this request.
HTTP 413 Content Too Large means the request body exceeds the size limit accepted by the server.
HTTP 414 URI Too Long means the target URI is longer than the server is willing or able to interpret.
HTTP 415 Unsupported Media Type means request payload format is not supported for this method or resource.
HTTP 418 I'm a Teapot comes from the HTCPCP joke protocol (RFC 2324) and is non-standard for production APIs.
HTTP 422 Unprocessable Content means the request syntax is valid but semantic validation fails for supplied instructions.
HTTP 431 Request Header Fields Too Large means the server rejects request headers because they are too large.
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Fix API payload issues faster by using 400 for malformed syntax and 422 for semantic validation failures, so clients correct format before business rules.
Playbook
Use this playbook to separate browser-enforced cross-origin policy failures from server-side CORS header and route defects and apply strict origin and credential controls safely.
Playbook
Use this playbook to separate malformed-request failures from semantic validation failures, then fix request contracts without broad server-side bypasses.
Contract expectations can change by version. If client and server versions drift, previously accepted fields or formats can become invalid.
Capture and diff full request payloads against a known-good example, then validate each field against the live API schema and constraints.
No. 400 is a broad class. Confirm whether the failure is contract validation, authentication syntax, or malformed transport metadata.