First time wasp user, Unable to add super simple custom API

api helloWorld {
  fn: import { helloWorld } from "@src/server/apis.ts",
  httpRoute: (GET, "/hello-world")
}

import { Request, Response } from 'express';

export const helloWorld = async (_req: Request, res: Response) => {
  res.setHeader('Content-Type', 'application/json');
  res.status(200).json({ message: "Hello World!" });
};