for app router, do return NextResponse.json({ message: 'hello from nextjs' }) instead

https://nextjs.org/docs/app/building-your-application/routing/route-handlers
this is the link for app router

i know this is solved, but i am assuming that you have changed page.tsx to route.ts to use route handlers (+ the other fixes Ray suggested)

Yup, thats what the documentation stated

just checking as others may not realise :)))