How to get response headers from fetch?

I have written the function notify() to send me a notification via discord when significant events occur. However discord has strict rate-limiting for such requests (Discord Developer Portal) and to avoid being rate-limited I need to consult the X-RateLimit-* parameters returned in the response headers. The problem I have found is that no headers are returned by the fetch() - see the output of my small test case below

Is there any way to access the response headers?

const myHeaders = new Headers({
      'content-type': 'application/json',
		  'User-Agent': 'DiscordBot ($url, $versionNumber)'
    });

// webhook from channel -> edit channel ->integrations -> webhooks
// Stored in environment variable.
const url = DISCORD_WEBHOOK;

addEventListener("fetch", (event) => {
  event.respondWith(
    handleRequest(event.request).catch(
      (err) => new Response(err.stack, { status: 500 })
    )
  );
});

async function handleRequest(request) {
  const { pathname } = new URL(request.url);

  if (pathname.startsWith("/api")) {
    promises=[...Array(10).keys()]
    r= await Promise.all(
      promises.map(item=>notify('testing '+item))
    )
    //s=r.map(item=>item.status)
    return new Response(JSON.stringify({ r }), {
      headers: { "Content-Type": "application/json" },
    });
  }

  return fetch("https://welcome.developers.workers.dev");
}

async function notify(msg) {
  const request = new Request(url, {
      body: JSON.stringify({ content: msg }),
      headers: myHeaders,
      method: 'POST',
  })
  return fetch(request).then(response=> response)
}

The results of the above are shown below

{"r":[{"webSocket":null,"url":"https://discord.com/api/webhooks/906321676348821535/HMBWXLQXIzkytGVRoVNy8DXpcZjKB9Vjv6xW0WQJlrjcIJpROwz7DnvfUVCP9qmrtlLF","redirected":false,"ok":false,"headers":{},"statusText":"Too Many Requests","status":429,"bodyUsed":false,"body":{"locked":false}},{"webSocket":null,"url":"https://discord.com/api/webhooks/906321676348821535/HMBWXLQXIzkytGVRoVNy8DXpcZjKB9Vjv6xW0WQJlrjcIJpROwz7DnvfUVCP9qmrtlLF","redirected":false,"ok":true,"headers":{},"statusText":"No Content","status":204,"bodyUsed":false,"body":null},{"webSocket":null,"url":"https://discord.com/api/webhooks/906321676348821535/HMBWXLQXIzkytGVRoVNy8DXpcZjKB9Vjv6xW0WQJlrjcIJpROwz7DnvfUVCP9qmrtlLF","redirected":false,"ok":true,"headers":{},"statusText":"No Content","status":204,"bodyUsed":false,"body":null},{"webSocket":null,"url":"https://discord.com/api/webhooks/906321676348821535/HMBWXLQXIzkytGVRoVNy8DXpcZjKB9Vjv6xW0WQJlrjcIJpROwz7DnvfUVCP9qmrtlLF","redirected":false,"ok":true,"headers":{},"statusText":"No Content","status":204,"bodyUsed":false,"body":null},{"webSocket":null,"url":"https://discord.com/api/webhooks/906321676348821535/HMBWXLQXIzkytGVRoVNy8DXpcZjKB9Vjv6xW0WQJlrjcIJpROwz7DnvfUVCP9qmrtlLF","redirected":false,"ok":true,"headers":{},"statusText":"No Content","status":204,"bodyUsed":false,"body":null},{"webSocket":null,"url":"https://discord.com/api/webhooks/906321676348821535/HMBWXLQXIzkytGVRoVNy8DXpcZjKB9Vjv6xW0WQJlrjcIJpROwz7DnvfUVCP9qmrtlLF","redirected":false,"ok":true,"headers":{},"statusText":"No Content","status":204,"bodyUsed":false,"body":null},{"webSocket":null,"url":"https://discord.com/api/webhooks/906321676348821535/HMBWXLQXIzkytGVRoVNy8DXpcZjKB9Vjv6xW0WQJlrjcIJpROwz7DnvfUVCP9qmrtlLF","redirected":false,"ok":false,"headers":{},"statusText":"Too Many Requests","status":429,"bodyUsed":false,"body":{"locked":false}},{"webSocket":null,"url":"https://discord.com/api/webhooks/906321676348821535/HMBWXLQXIzkytGVRoVNy8DXpcZjKB9Vjv6xW0WQJlrjcIJpROwz7DnvfUVCP9qmrtlLF","redirected":false,"ok":false,"headers":{},"statusText":"Too Many Requests","status":429,"bodyUsed":false,"body":{"locked":false}},{"webSocket":null,"url":"https://discord.com/api/webhooks/906321676348821535/HMBWXLQXIzkytGVRoVNy8DXpcZjKB9Vjv6xW0WQJlrjcIJpROwz7DnvfUVCP9qmrtlLF","redirected":false,"ok":false,"headers":{},"statusText":"Too Many Requests","status":429,"bodyUsed":false,"body":{"locked":false}},{"webSocket":null,"url":"https://discord.com/api/webhooks/906321676348821535/HMBWXLQXIzkytGVRoVNy8DXpcZjKB9Vjv6xW0WQJlrjcIJpROwz7DnvfUVCP9qmrtlLF","redirected":false,"ok":false,"headers":{},"statusText":"Too Many Requests","status":429,"bodyUsed":false,"body":{"locked":false}}]}