next.js/examples/cms-prismic/pages/api/preview.ts

import { NextApiRequest, NextApiResponse } from "next";
import { setPreviewData, redirectToPreviewURL } from "@prismicio/next";

import { createClient } from "../../lib/prismic";

export default async function preview(
  req: NextApiRequest,
  res: NextApiResponse,
) {
  const client = createClient({ req });

  setPreviewData({ req, res });

  await redirectToPreviewURL({ req, res, client });
}