rsnext/examples/custom-routes-proxying/next.config.js

module.exports = {
  async rewrites() {
    return [
      // we need to define a no-op rewrite to trigger checking
      // all pages/static files before we attempt proxying
      {
        source: '/:path*',
        destination: '/:path*',
      },
      {
        source: '/:path*',
        destination: `https://custom-routes-proxying-endpoint.vercel.app/:path*`,
      },
    ]
  },
}