Error: The Middleware "/middleware" must export a middleware or a default function

[bovealexandre]

Summary

I have a problem with middleware in the last version of next.js, I get this error every time.

Error: The Middleware "/middleware" must export a `middleware` or a `default` function

and in the console, this one :

⨯ Error: The Middleware "/middleware" must export a `middleware` or a `default` function
    at <unknown> (edge-wrapper.js:2:6)
  1 | self._ENTRIES ||= {};
> 2 | const modProm = import('MODULE');
    |      ^
  3 | modProm.catch(() => {});
  4 | self._ENTRIES["middleware_middleware"] = new Proxy(modProm, {
  5 |     get(modProm, name) {
 GET / 404 in 4ms

Additional information

import createIntlMiddleware from 'next-intl/middleware'
import { NextRequest } from 'next/server'
import { locales } from '@i18n/routing'

export default async function middleware(request: NextRequest) {
    const headerLocale = request.headers.get('x-test-locale')
    const defaultLocale = (headerLocale ?? locales[0]) as (typeof locales)[number]

    const handleI18nRouting = createIntlMiddleware({
        locales: locales,
        defaultLocale: defaultLocale
    })
    const response = handleI18nRouting(request)

    response.headers.set('x-test-locale', defaultLocale)

    return response
}

export const config = {
    matcher: ['/((?!api|_next/static|_next/image|favicon.ico|sitemap.xml|robots.txt).*)']
}

### Example

_No response_

[osvalda]

Where is your middleware stored? In your root folder? Do you have app or src packages?
If any of them exist then you have to store your middleware within too.

[Victor-Nyagudi]

Moving the middelware.ts file into the app folder fixed my problem.