Schema, contract, and parameter constraint validation failures.
Last reviewed: March 2, 2026|64 mapped errors|Page 5 of 5
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 (64 total). Showing 61-64.
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 424 Failed Dependency means the request could not complete because a dependent action failed first.
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.