# MALFORMED_REQUEST_HEADER

The `MALFORMED_REQUEST_HEADER` error signifies that a request made to the server includes a header that is incorrectly formatted or contains invalid data. This could be due to syntax errors, incorrect header field names, or incompatible header values.

## Troubleshoot

To troubleshoot this error, follow these steps:

1. **Inspect request headers**: Review the headers in your request. Ensure that they are correctly formatted and adhere to the [HTTP standard](https://developer.mozilla.org/en-US/docs/Glossary/Request_header)
2. **Validate UTF-8 encoding**: Confirm that all request headers, especially cookie values, are valid UTF-8 strings. Non-UTF-8 characters in headers, particularly in the cookie header, often cause this error
3. **Examine Vercel Function behavior**: Since this error is specific to Vercel functions, verify the functionality and responses of your Vercel functions. Ensure they are correctly handling request headers and not contributing to malformed responses


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title: "MICROFRONTENDS_MIDDLEWARE_ERROR"
description: "The microfrontend middleware returned an invalid application."
last_updated: "2026-02-03T02:58:42.056Z"
source: "https://vercel.com/docs/errors/MICROFRONTENDS_MIDDLEWARE_ERROR"
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