Error map
1040 Cloudflare Error 1040 / 1041: Invalid request header modification
Cloudflare · layer 3, Edge & web server
Centre: this error. First ring: errors it is linked with (12). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (12)
CORS Error: No 'Access-Control-Allow-Origin' header is present
The browser blocked a cross-origin request because the server’s response didn’t include the CORS headers allowing your site’s ori…
Warning: session_start(): Session cannot be started after headers have already been sent
session_start() ran after output was sent, so PHP can’t set the session cookie.
HTTP 411 Length Required
The server refuses a request with a body but no Content-Length header.
Unexpected characters at the top of the page / headers already sent by BOM
A UTF-8 byte-order mark (BOM) at the start of a PHP file is sent as output, breaking headers, JSON and images.
HTTP 100 Continue
An interim response telling the client to go ahead and send the request body — normal when the client sent Expect: 100-continue.
Cloudflare Error 1035 / 1036: Invalid request rewrite (invalid URI path / query string)
A Transform Rule (URL rewrite) produced an invalid path or query string.
Warning: Cannot modify header information - headers already sent
You called `header()`, `setcookie()` or `session_start()` after output had already been sent to the browser.
Refused to load the script because it violates the following Content Security Policy directive
The page’s Content-Security-Policy doesn’t allow that script, style, image or connection source.
HTTP 103 Early Hints
An interim response that sends Link headers early so the browser can preload CSS, fonts or scripts while the server is still buil…
HTTP 417 Expectation Failed
The server or a proxy can’t meet the Expect header in the request — almost always Expect: 100-continue.
Cloudflare Error 1037: Invalid rewrite rule (failed to evaluate expression)
A rewrite rule’s dynamic expression failed at runtime — for example a function received a value of the wrong type or a missing fi…
HTTP 428 Precondition Required
The server requires a conditional request (If-Match / If-Unmodified-Since) to prevent lost updates, and you didn’t send one.
Two steps away (34)
AWS S3: AccessDenied (403) when calling GetObject / PutObject
An IAM policy, bucket policy, ACL/ownership setting, Block Public Access or KMS key policy denied the S3 request.
HTTP 401 Unauthorized
The request has no valid authentication credentials — you need to log in or send a valid token.
HTTP 403 Forbidden
The server understood the request but refuses to authorize it — you (or the server process) are not allowed to access this resour…
AWS: ExpiredToken — The security token included in the request is expired
Temporary AWS credentials (STS/SSO/assumed role) have expired.
Warning: session_start(): open(/var/lib/php/sessions/sess_x, O_RDWR) failed: Permission denied
PHP can’t write session files to the configured session.save_path.
HTTP 416 Range Not Satisfiable
The client asked for a byte range (Range: bytes=…) that lies outside the file — usually a resumed download of a file that changed…
HTTP 400 Bad Request
The server could not understand the request because its syntax, headers or body are malformed or invalid.
HTTP 413 Content Too Large (Request Entity Too Large)
The request body is bigger than the server is willing to accept — usually a file upload over the configured limit.
API Error: Missing required parameter (parameter_missing / "x" is required)
The API rejected the request because a field it requires — in the query string, path, headers or JSON body — wasn’t sent or was e…
URIError: URI malformed
decodeURIComponent/decodeURI received an invalid percent-encoded sequence.
UnicodeEncodeError: 'charmap' codec can't encode character '\u2192'
Python tried to write text in an encoding that can’t represent some characters — common in Windows consoles and files opened with…
HTTP 505 HTTP Version Not Supported
The server doesn’t support the HTTP protocol version used in the request.
WordPress: The link you followed has expired
Usually an upload (theme, plugin, media) larger than PHP’s upload/post limits — WordPress receives an empty request and shows thi…
Upload error: File type not allowed / unsupported file type
The upload was rejected because the file’s type — extension, MIME type or actual content — isn’t on the allowed list.
Cloudflare Error 1000: DNS points to prohibited IP
A proxied DNS record points at a Cloudflare IP address, creating a loop.
Cloudflare Error 1001: DNS resolution error
Cloudflare received the request but the hostname isn’t set up on Cloudflare (or the domain was just added and not active yet).
Cloudflare Error 1002: DNS points to Prohibited IP / Restricted
A record points to a private, reserved or Cloudflare IP that Cloudflare won’t proxy to.
HTTP 500 Internal Server Error
The server hit an unexpected condition — usually an unhandled exception or misconfiguration in the application.
PHP Fatal error: Uncaught Error: Call to undefined function
PHP can’t find the function you called — usually a missing extension, missing include, or namespace issue.
Warning: Undefined array key / Undefined index
Your code reads an array key that doesn’t exist — common with `$_GET`, `$_POST` and decoded JSON.
Mixed Content: The page was loaded over HTTPS, but requested an insecure resource
An HTTPS page tried to load a script, API or image over plain HTTP, and the browser blocked (or warned about) it.
SecurityError: Blocked a frame with origin "x" from accessing a cross-origin frame.
Script tried to read or modify an iframe (or window) from another origin.
Script error. (at line 0) — cross-origin error details hidden
An error happened in a script from another origin, and the browser hid the details.
HTTP 504 Gateway Timeout
A proxy or gateway waited too long for the upstream server to respond and gave up.
Cloudflare Error 524: A Timeout Occurred
Cloudflare connected to the origin, but the origin didn’t send an HTTP response within 100 seconds.
HTTP 304 Not Modified
The cached copy is still valid, so the server sends no body and the client reuses its cache.
HTTP 407 Proxy Authentication Required
A proxy between you and the server requires credentials before it will forward your request.
Upload error: File too large (LIMIT_FILE_SIZE / file exceeds maximum upload size)
The uploaded file is larger than the limit set by the API, framework or server.
Upload error: checksum mismatch (BadDigest / Content-MD5 did not match / XAmzContentSHA256Mismatch)
The server computed a different checksum for the data it received than the one your client declared, so it rejected the upload as…
Cloudflare Error 1003: Direct IP access not allowed
The request went to a Cloudflare IP address directly (or with a Host header for a domain not on Cloudflare).
Cloudflare Error 1004: Host Not Configured to Serve Web Traffic
The DNS record was just created or changed and Cloudflare hasn’t propagated it yet — or Spectrum/non-HTTP ports are involved.
HTTP 409 Conflict
The request conflicts with the current state of the resource — e.g. a duplicate or an edit based on an outdated version.
java.lang.InterruptedException (sleep interrupted)
A blocked thread (sleep, wait, join, queue take) was interrupted by another thread.
java.util.concurrent.TimeoutException
A Future.get(timeout) or async operation didn’t complete in the allowed time.
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