Comment-to-DM describes taking a conversation that began as a public comment on a Facebook or Instagram ad and continuing it as a private message. On Meta's platforms this is done through a private reply — a message a Page can send privately in response to a comment, within the policy window Meta defines for it.
It is a natural fit for buyer-intent comments. When someone comments "is this still available?" under your ad, a private reply lets you answer with details — pricing, links, stock — without conducting the whole sale in public, while still acknowledging the public comment so others see you are responsive.
The important constraints are honesty and policy. Private replies are only permitted within Meta's rules and timing window, and they should never feel like spam. ROAS Shield will draft a private reply for a buyer-intent comment once Meta approves the pages_messaging permission — that capability isn't live yet. Today, ROAS Shield drafts public replies. When comment-to-DM ships, every message will be draft-first, requiring a person to approve it before it sends — never auto-sent, even with a rule enabled. (Public comment replies can optionally auto-send once you opt in and the model's confidence and safety checks pass; direct messages never will.)
For the wider conversion picture, see how to turn ad comments into customers, and for the public-reply version, how to reply to Facebook ad comments.