Comment-to-DM automation, as an API.

// comment.received -> private reply, the whole flow.
// Acknowledge first: the send calls Meta, so do it after you respond.

const KEYWORD = /\blink\b/i;

app.post('/webhooks/outstand', async (req, res) => {
  if (!verifySignature(req)) return res.sendStatus(401);
  res.sendStatus(200); // ack fast, then work

  if (req.body.event !== 'comment.received') return;

  const c = req.body.data;
  // parentCommentId is null for a top-level comment.
  if (c.parentCommentId || !KEYWORD.test(c.text ?? '')) return;

  // Instagram needs the author id; Facebook replies to the comment alone.
  const addressing =
    c.network === 'instagram'
      ? { instagram: { comment_id: c.commentId, author_id: c.authorId } }
      : { facebook: { comment_id: c.commentId } };

  await fetch('https://api.outstand.so/v1/conversations', {
    method: 'POST',
    headers: {
      Authorization: `Bearer ${process.env.OUTSTAND_API_KEY}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      social_account_id: c.accountId,
      content: `Thanks @${c.authorUsername}! Here it is: https://shop.example.com/blue`,
      ...addressing,
    }),
  });
});

// 201 Created returns the conversation and its first message. Store
// conversation.id against c.commentId so the reply lands in the right thread.

Three fields off the webhook address the DM: accountId becomes social_account_id, commentId becomes instagram.comment_id, and authorId becomes instagram.author_id. On a Facebook Page the comment id alone is enough. Full reference in Start a conversation.