next.js/errors/next-start-serverless.md

Using next start with target not set to server

Why This Error Occurred

Next.js can only handle running a server when the target is set to server (this is the default value). A serverless build, for instance, has no handler for requests–this is usually implemented by a hosting provider.

Possible Ways to Fix It

Use a different handler than next start when testing a serverless production build, otherwise just use next dev.