How to Auto-Reply to Instagram Comments via API

The auto-reply loop

Three pieces: a webhook that delivers new comments, logic that decides the reply, and one POST that sends it.

Postproxy syncs comments on your published posts and fires a comment.created webhook for each new one. Your handler replies through the Comments API — the same endpoints work on Instagram, Facebook, and Threads.

Reply to a comment

curl -X POST "https://api.postproxy.dev/api/posts/POST_ID/comments?profile_id=PROFILE_ID" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "body": "Sizes run true — check the chart in our bio link.",
    "parent_id": "COMMENT_ID"
  }'

parent_id accepts the Postproxy hashid or Instagram’s native comment ID. Omit it to comment on the post itself. The reply is created with status: "pending" and published asynchronously; once live, external_id and permalink are populated.

Instagram comments are text-only — media in a reply returns an error. Captions max out where Instagram caps them, so keep replies short anyway.

The webhook handler

app.post("/webhooks/postproxy", async (req, res) => {
  res.sendStatus(200);

  const event = req.body;
  if (event.type !== "comment.created") return;

  const c = event.data.object;
  if (c.platform !== "instagram") return;
  if (c.author_external_id === MY_PROFILE_EXTERNAL_ID) return; // never reply to yourself

  const reply = decideReply(c.body); // your logic: keyword map, FAQ matcher, LLM
  if (!reply) return;

  await fetch(
    `https://api.postproxy.dev/api/posts/${c.post_id}/comments?profile_id=${PROFILE_ID}`,
    {
      method: "POST",
      headers: {
        Authorization: `Bearer ${process.env.POSTPROXY_API_KEY}`,
        "Content-Type": "application/json",
      },
      body: JSON.stringify({ body: reply, parent_id: c.id }),
    }
  );
});

The self-check matters: your own replies also sync and fire comment.created. Skip anything authored by your profile or you’ve built an infinite loop with yourself.

Decide who gets a reply

Each synced comment carries author signals in metadata, fetched from Meta after ingestion:

• is_verified_user — verified account
• follower_count — author’s audience size
• is_user_follow_business / is_business_follow_user — follow relationship

A common policy: auto-reply to questions, route verified or high-follower authors to a human, and hide anything that trips your spam filter.

Backfill and audit with list

Webhooks are the real-time path; GET covers everything else — backfills after downtime, dashboards, reply audits:

curl "https://api.postproxy.dev/api/posts/POST_ID/comments?profile_id=PROFILE_ID&per_page=50" \
  -H "Authorization: Bearer YOUR_API_KEY"

Top-level comments are paginated; each carries a flat replies array with parent_external_id preserved, so threads reconstruct cleanly.

What works where

Unsupported actions return 405, so a cross-platform handler can just try and fall through.

Going further

• Turn a comment into a DM with a private reply — the highest-converting follow-up to a public reply.
• Auto-hide spam and slurs with the moderation guide.
• Full field reference and error shapes: Comments API.