What about comments from before the automation?

Meta lets an Instagram account send one private reply to a comment, and that reply has to go out within 7 days of the comment. A comment older than that cannot receive a DM through the private-reply API. Replier only DMs comments it has stored. It doesn't DM people who commented before the automation existed, unless Replier stored that comment in the last 7 days and you choose Send replies or Catch up. It doesn't DM people whose comments it never stored: comments from before the account was connected, or ones Instagram never delivered and the 15-minute check didn't recover.

For those older comments, the practical path is a public reply under the comment that asks the person to comment the keyword again, or to DM you. A new comment is a new private reply, and a normal automation can answer it.

Catch up lists comments and messages Replier received but has not already handled. A comment can appear within 7 days of the comment, and a message or Instagram story reply within 24 hours. It does not search the whole inbox, and it does not recover interactions from before the account was connected. Open “Catch up”, review the list, and select “Reply to” with the number of replies. That sends the automation’s saved replies — the DM, and the public reply when one is saved — and it counts toward the interaction allowance. On the Free plan, that allowance is 100 interactions a month.

Replier may also show a prompt titled “Reply to recent matching comments?” when you turn an automation on, save it after adding a specific post or changing its keywords, or resume one that targets a specific post (“Resume automation”). It only lists matching comments Replier already stored in the last 7 days, on that specific post, that have not been replied to. “Send replies” sends that automation’s saved replies, the same way a new matching comment would. “Skip” leaves them. “All posts” and “Next post” do not open this prompt until a specific post is selected. When a post has more than the batch can start, the prompt adds “We'll start with the first” and the number; that batch is 100 comments per post.

Instagram sometimes never delivers a comment. Every 15 minutes, Replier reads comments on posts an active automation watches and replies to ones it has no event for. A comment is recovered only if it was posted after the automation was added or last saved, after the account connected, within the last 7 days, and at least 10 minutes ago. It covers post comments, not story replies or messages. The public reply and DM go out as usual and count toward the interaction allowance.

Select “Turn on automation” before you publish, and put the keyword in the caption. Or set the target to “Next post”: the next published post uses this automation, so comments on that post are answered as they arrive.

“All posts” replies to new comments on every post, including older posts, from the moment it is active. It does not DM comments that were already on the post.