4xx Client Error Overview

4xx codes are error responses indicating issues on the client's end, often due to network problems. These codes can be used as a response to any request method and usually come with an explanation from the origin server, except for HEAD requests.

• Custom Rules: Can return any response code in the 400 to 499 range if configured by the site owner.
• Significance: Indicates that the client sent a request that could not be understood or processed due to issues with the request itself.

Specific 4xx Status Codes

400 Bad Request

• Causes: Malformed request syntax, invalid content, message framing problems, or deceptive routing (e.g., special characters not URL encoded).
• Resolution: Ensure correct syntax and proper authentication when using Cloudflare API.

401 Unauthorized

• Causes: Client fails to provide valid authentication credentials.
• Resolution: Provide correct authentication credentials and check the WWW-Authenticate header for guidance.

402 Payment Required

• Reserved for future use and not implemented.

403 Forbidden

• Causes: Insufficient permissions to access a resource; can be due to server configuration or Cloudflare WAF/Security settings.
• Resolution: Check server permission rules and ensure Cloudflare's IPs aren't blocked.

404 Not Found

• Causes: Resource not found due to mistyped URLs, broken links, or removed pages.
• Resolution: Implement a custom 404 page for improved user experience.

405 Method Not Allowed

• Causes: Unsupported HTTP method used in the request.
• Resolution: Verify that the correct methods are enabled on the origin server.

406 Not Acceptable

• Causes: Resource not available in the requested format (e.g., language or charset).
• Resolution: Origin server should serve a less preferred format if possible.

407 Proxy Authentication Required

• Causes: Missing authentication credentials for a proxy server.
• Resolution: Include appropriate Proxy-Authorization header.

408 Request Timeout

• Causes: Client fails to send a complete request within the server's timeout period.
• Resolution: Check the origin server's timeout settings and client’s connection stability.

409 Conflict

• Causes: Request conflict with the current state of the resource (e.g., simultaneous edits).
• Resolution: Server should provide information to resolve conflict.

410 Gone

• Causes: Resource permanently removed.
• Resolution: Remove links to the resource; contact hosting provider for assistance.

411 Length Required

• Causes: Missing Content-Length in request headers.
• Resolution: Resend request with the required header.

412 Precondition Failed

• Causes: Resource does not meet conditions set by the client.
• Resolution: Refer to ETag headers and resolve condition issues.

413 Payload Too Large

• Causes: Request payload exceeds server's size limit.
• Resolution: Split requests into smaller chunks or upgrade plan for larger uploads.

414 URI Too Long

• Causes: Excessively long URI.
• Resolution: Simplify the URI.

415 Unsupported Media Type

• Causes: Unsupported payload format.
• Resolution: Check Content-Type or Content-Encoding headers.

416 Range Not Satisfiable

• Causes: Invalid Range header in request.
• Resolution: Ensure requested range does not exceed resource bounds.

417 Expectation Failed

• Causes: Expect header requirements not met.
• Resolution: Avoid unsupported Expect headers.

429 Too Many Requests

• Causes: Too many requests in a short time frame.
• Resolution: Abide by rate limits and check Retry-After header.

451 Unavailable For Legal Reasons

• Causes: Legal restrictions blocking resource access.
• Resolution: Check response explanation for details.

499 Client Closed Request

• Causes: Client terminates connection before server response.
• Resolution: Ensure TCP connection is established and timeout settings are appropriate.