api/newsletter.ts inside your next.js project

newsletter.ts

// Full code here: https://github.com/riccardogiorato/qstash-with-nextjs
import type { NextApiRequest, NextApiResponse } from "next";

type ResponseEmailNewsletter =
  | {
      error: string;
    }
  | {
      message: string;
    };

export default async function handler(
  req: NextApiRequest,
  res: NextApiResponse<ResponseEmailNewsletter>
) {
  // reject if not POST
  if (req.method !== "POST") {
    return res.status(405).json({ error: "Method not allowed" });
  }

  // reject if no email
  if (!req.body.email) {
    return res.status(400).json({ error: "Email is required" });
  }

  // record email in database from req.body.email
  const { email } = req.body;

  // send email to database
  // prisma.newsletter.create({
  //   data: {
  //     email,
  //   },
  // });

  // await 5 seconds
  await new Promise((resolve) => setTimeout(resolve, 5000));

  // randomly fail the request
  if (Math.random() < 0.5) {
    return res.status(500).json({ error: "Internal server error" });
  }

  console.log(`Newsletter active for ${email}`);

  res.status(200).json({ message: `Newsletter active for ${email}` });
}