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1040

Error 1040: Invalid request rewrite (header modification not allowed)

Alternative forms: Error 1040

What does this code mean?

Code 1040 · An issue reported by Cloudflare HTTP errors.

Official explanation · Original text

This error indicates that an attempt was made to modify a restricted HTTP header. You are trying to modify an HTTP header that Request Header Transform Rules cannot change.

Troubleshooting and diagnostic links

First check that the document's product, version, and environment match your situation.

Source and terms of use

Error 1040: Invalid request rewrite (header modification not allowed) ↗

Creator: Cloudflare, Inc. and contributors
License: Creative Commons Attribution 4.0 International
Checked on: 2026-11-12

Modifications: Selected introductory official description; Markdown stripped; original Korean product context added. Direct official error page retains the complete cause and resolution instructions.

Source details · Original licenses and notices