const response = await fetch(
  "https://api.socialfetch.dev/v1/substack/posts/https%3A%2F%2Fwww.astralcodexten.com%2Fp%2Fopen-thread-400/comments",
  {
    headers: {
      "x-api-key": "YOUR_API_KEY"
    }
  }
);

const data = await response.json();
console.log(data);