Starts the flow on comments under posts, reels and live videos. Post selection, excluded words, replies and Meta's rules for the first message are all covered one by one.
One of your posts took off and hundreds of "price?" comments landed under it. Answering each one by DM by hand takes more than a day, and the people who commented first hear back last. The Post comment trigger takes that job over: it catches the comment, sends a private message to whoever wrote it, and if you want, posts a public answer under the comment as well. This guide covers every field, Meta's rules for the first message out of a comment, and the traps in the setup.
⚠️ Note: this trigger works on Instagram only. WhatsApp has no posts and no comments, so the type list never shows it on a WhatsApp account. If it is sitting in a saved flow, the pre-publish check warns "Comment, mention, story and share triggers only work on Instagram".
In this article you will find:
What it does
Building the trigger
Fields and buttons
Rules for the first message out of a comment
Priority: which comment trigger wins
Limits and known issues
Common mistakes and how to fix them
What it does
The trigger listens to comments on your account's posts, reels and live videos. When a comment matches your settings, the flow starts and a session opens for the person who wrote it.
The flow's first message goes privately to the commenter. This is Meta's "private reply to a comment" route: the message goes through even if the person has never sent you a DM, because writing a comment counts as permission. Details are in the section below.
The public answer posted under the comment is no longer part of the trigger. It is its own step: add Reply to comment to the flow. The note in the editor says the same thing: "The reply posted under the comment is now its own step: 'Reply to comment'."
Your account's own comments never trigger anything. That is deliberate: if our own public answer re-ran the trigger, the flow would feed its own queue and loop forever.
Building the trigger
Let us build a "price list" flow for a furniture shop.
Open an empty flow with New automation from the Automations list.
On the Flow tab, click the When… box on the canvas.
Press Add trigger in the panel on the side.
Pick Post comment from the list.
Set the Where list to Posts and reels, so your live videos stay out of this flow.
Press Choose post in the Post field and pick the sofa-set post.
Type price and how much into the Keywords box, pressing Enter after each.
Type expensive into the Excluded words box; you do not want a price list going out on a complaint.
Leave the Replies also trigger checkbox off.
Connect the start box's Next output to a Message step and write the price information as plain text.
Add a Reply to comment step to the canvas and write "Sent the prices by DM 💬".
Press Publish at the top right. Your automation is now running.
Once it is live, test it by commenting from another account rather than your own: your own comment does not trigger.
Fields and buttons
The trigger card holds six fields and a remove button.
Where — Where the comment came from. Three options:
All comments: both post/reel and live video comments.
Posts and reels: only comments on feed posts and reels.
Live video: only comments written during a live video.
Narrowing the source gives the trigger 1 specificity point; see the priority section below.
Post — Which post's comments to listen to. Left empty, every post on the account is listened to; the hint under the field says so: "Comments on every post of the account." When your Instagram account is connected the field shows a Choose post button; otherwise it becomes a plain box where you paste an ID.
The post picker
Choose post opens a window listing your posts with their covers.
Type into the Search posts box at the top and the list filters itself; there is no separate search button.
Refresh pulls the list from Instagram again. If it cannot be refreshed you see "The list could not be refreshed from Instagram; showing the most recent copy."
The first cell of the grid is All posts; tapping it clears the selection.
Posts carrying the Comments off badge are dimmed. An automation never fires on those.
The Deleted badge marks a post that no longer appears in the Instagram list but was selected earlier.
Previous and Next at the bottom of the window move between pages.
After you choose, the post's cover and caption appear above the field; Clear selection undoes it.
Keywords — The words to look for in the comment. Left empty, every comment triggers. Added with Enter or a comma, up to 30 words, each up to 100 characters.
Match — How the word is looked for in the comment: Contains, Whole word, Starts with, Exact match. The default is Contains and the mode applies to every word on the list. Details are in the match modes article.
Excluded words — If the comment contains one of these, the flow does not start. Use it for profanity, a competitor's name or words like "cancel". This list is always matched with "contains"; the Match setting above does not apply to it. Up to 30 words.
Replies also trigger — When off, only top-level comments on the post trigger. Turning it on lets a reply written under our own answer start a new flow and cut the ongoing chat. The default is off and it should stay off on most accounts: left on, a second DM goes out in the person → us → person chain.
Channel — Which account the trigger runs on. It appears only when more than one channel is connected.
Remove — The cross at the top right of the card deletes the trigger.
Rules for the first message out of a comment
The first message of a comment-started flow is not an ordinary DM; it goes through Meta's private reply route. That route has three rules, all of them on Meta's side:
Once per comment. Only one private reply may be sent for a comment. When the flow sends a second message, ordinary DM rules apply again: if the person has not written in the last 24 hours, that message does not go out.
Within 7 days of the comment. A private reply cannot be sent for a comment older than that.
Plain text only. A private reply carries no buttons, cards, list rows or files.
That last rule is the most misunderstood one. If you put buttons in the first message, the pre-publish check warns: "In a flow that starts from a comment the first message can only be plain text (Meta's rule): if the person hasn't written in the last 24 hours, buttons, cards and list rows are dropped." A step that sends a file gets its own warning. The fix is simple: keep the first message plain text and put the step with buttons or a file after the person replies.
💡 If the person has already sent you a DM within the last 24 hours, the messaging window is open and these restrictions do not apply; the message goes out with all its buttons. They only kick in while the window is closed.
One more warning: if you put a Delete comment action in the flow and then try to send a message, the message does not go out. Deleting the comment also uses up the private reply allowance. Send the message first and leave deletion for last.
Live video comments add one more case: once the broadcast has ended, no private reply can be sent. The logs show that as "Live video ended".
Priority: which comment trigger wins
One comment may match several triggers. A specificity score picks the winner, and the narrower one wins:
Choosing a post: 10 points. The heaviest narrowing there is.
Match mode: 1–4 points. Exact match 4, whole word 3, starts with 2, contains 1.
Narrowing the source: 1 point. Posts only, or live only.
For example: "every comment on this campaign post" scores 10, while "all posts + the word price (contains)" scores 1. A "price?" comment landing on the campaign post runs the first one. On a tie the trigger created first wins.
The comment trigger is an explicit trigger: it cuts the person's running session and starts this flow. Flows whose interruption setting is turned off on the Settings tab are shielded from that.
One important distinction: a comment is not a chat. If no comment trigger matches — because of an excluded word, because it is a reply, or because it landed on a different post — the comment's text is not handed to the person's running DM flow and nothing happens. Keyword and default reply triggers are not tried either.
Limits and known issues
The trigger works on Instagram only (a limit on Meta's side: WhatsApp has no comments).
The keyword and exclude lists each take up to 30 words, each up to 100 characters.
The exclude list is always matched with "contains"; its mode cannot be changed.
If the same word is in both the match and the exclude list the trigger can never fire; the pre-publish check warns about it.
If comments are off on the selected post the trigger never runs; the check warns "Comments are turned off on the selected post".
If the selected post has been deleted you see "The selected post was not found on the Instagram account".
A private reply may be sent once per comment and within 7 days of it, and carries plain text only.
The account's own comments do not trigger.
The comment event does not fall back to message triggers.
The trigger only runs while the automation is Live.
Common mistakes and how to fix them
Putting buttons in the first message. With the window closed the buttons are dropped and the customer sees only text. Move the buttons to the second step.
Forgetting to choose a post. With the field empty the trigger listens to every post on the account, so a "price" comment on an old post also starts your new campaign flow. Always pick the post in campaign flows.
Turning replies on. With it on, even a "thanks" written under our own answer restarts the flow and cuts the ongoing chat. Leave it off.
Leaving the exclude list empty. On a viral post, complaints and profanity trigger too. Add words like a competitor's name, "expensive" or "scam".
Deleting the comment first. The message after a Delete comment action does not go out. Order it message → reply → delete.
Forgetting the Reply to comment step. If you only send the private DM, the space under the post stays empty and your other followers do not see that you answered. Add the Reply to comment step.
Testing from your own account. Your own comment does not trigger; test with another account or with the simulator on the Test tab.
If you have done all of this and the flow still does not start, see the no reply is posted under the comment guide or get in touch with our Support team.