How do I create a comment with reddit's api using fetch?

Question

async function commentOnRedditPost(postId, commentText, accessToken) {
 const url = `https://oauth.reddit.com/api/comment`;
 // const params = new URLSearchParams();
 console.log("access_token:", accessToken, postId, commentText);
 // params.append("parent", postId); // 'thing_id' is used instead of 'parent'
 // params.append("text", commentText);
 const response = await fetch(url, {
 method: "POST",
 headers: {
 Authorization: `Bearer ${accessToken}`,
 "Content-Type": "application/json",
 Accept: "text/html",
 "User-Agent": "profullstack comment bot v1.0",
 "Sec-Fetch-Dest": "document",
 "Sec-Fetch-Mode": "navigate",
 "Sec-Fetch-Site": "cross-site",
 },
 mode: "cors",
 body: JSON.stringify({
 api_type: "json",
 thing_id: postId,
 text: commentText,
 }),
 });
 if (!response.ok) {
 console.error(await response.text());
 }
 return response.json();
}

I get a 403 and a body parsing error:

{"message": "Forbidden", "error": 403}
Failed to comment on Reddit post 1cxbmk6: TypeError: Body is unusable

Answer 1

Needed to use thing_id: post.name, instead of postId. It includes the "type" ie: t3_$id