MIDDLEWARE_INVOCATION_FAILED

What it means in plain English

Vercel documents MIDDLEWARE_INVOCATION_FAILED as an issue with Routing Middleware being invoked on the CDN. The page says this includes unhandled exceptions. The response it shows is Internal Server Error.

A function 500 with FUNCTION_INVOCATION_FAILED is a different Vercel error. See Vercel 500: FUNCTION_INVOCATION_FAILED.

Likely causes

• The middleware function throws, and that exception is not handled.
• The middleware code loops.
• The CDN itself is having an outage. Vercel says to check the status page after the steps below.

How to fix it, step by step

1. Open the application logs. Vercel says they are at the host URL under the /_logs path, and to look for errors from Routing Middleware being invoked.
2. Read the exception in that log and fix it in the middleware code.
3. Check the middleware for an infinite loop. Vercel lists that next to other errors in the function code.
4. If the logs are clean and the error continues, check Vercel's status page for a CDN outage, which Vercel says can cause this error.
5. A Clerk message that clerkMiddleware() was not detected is Clerk's own error. See Clerk: auth() was called but clerkMiddleware() was not detected.

How to check it worked

• The route that returned Internal Server Error now returns the page.
• /_logs no longer records MIDDLEWARE_INVOCATION_FAILED for that request.

Sources

• https://vercel.com/docs/errors/middleware_invocation_failed (opens in a new tab)