What are Instagram's rules for replying privately to a comment?

A business can send one private message in reply to a comment, within seven days of the comment being posted. It can only send more after the person replies, and then within 24 hours of their reply. On a live video, private replies only work while the broadcast is running.

These rules come from Meta's developer documentation for private replies, and every comment-to-DM tool has to follow them. The private reply includes a link back to the post the comment was on, and it lands in the person's main inbox if they follow the account, or in message requests if they don't.

For agencies this means:

• Comment-to-DM campaigns work best in the first few days after a post goes up.
• If a client asks why an older post's "comment for the link" stopped working, this is usually why.
• Because the reply is tied to a specific comment on a specific post, conversations that start this way can be linked to that post automatically, which makes them some of the best-attributed leads you'll have.

The full method is in How to Tell Which Instagram Post a DM Came From (What Meta Tells You, and What It Doesn’t).