Somewhere in your application, you imported next directly which is only meant to be used with legacy custom servers.

You should not import next inside of pages or components.

Ensure any usage of import next from "next" is specific to custom server usage and isn't included in your pages or components.

Also ensure any type imports are kept inside of TypeScript files e.g. ensure import { PageConfig } from 'next' isn't used in JavaScript files.

• Custom Server Documentation