If a Reel blew up and you got roughly 15,000 comments in a few hours but your comment-to-DM tool only sent around 3,000 messages, nothing is broken. This is Meta's plumbing showing through, not ManyChat doing something weird. Here is exactly what is going on, point by point.
1. The rate limit and the queue
Comment private replies are capped per account on Meta's side. The documented ceiling is 750 per hour per account, and most tools deliberately throttle under that to stay ban-safe. When a spike pushes you past the cap, a well-built tool does not drop the excess at the rate-limit layer. It holds it in a queue and sends it as the rolling hour frees up. That is why a 15,000-comment burst trickles out over the following hours instead of landing all at once.
2. Are people getting silently skipped?
A send that fails on a genuine rate-limit error should be retried, not silently thrown away. So the rate limit itself is usually not what loses people.
The quieter loss is Meta's own hiccups. Every so often a private reply comes back with a temporary error, a 500 or an "unexpected internal error", that would go through fine if you tried again a minute later. A tool that tries once, or three times in a few seconds, and then moves on loses that person without telling anyone. Ask your tool what it does with a failed send. The right answer is: keep retrying until Meta says it can never work, and do it inside the window in the next point, which is the one almost everyone gets wrong.
3. The window is 7 days, not 24 hours
The initial private reply to a comment has a 7-day window on Meta's side, not 24 hours. The 24-hour window you have probably read about is for continuing a conversation after someone replies to you. For the first comment-to-DM, you have a full week.
That is good news, you have far more runway than you thought. The catch: the window only helps if the send is still waiting somewhere. At 750 per hour, 15,000 DMs clear in about 20 hours, well inside a week, so if people are still missing days later, their sends were dropped or never queued, not just delayed. Anyone still unreached more than 7 days after their original comment becomes unreachable by private reply.
4. Best practices for viral-level volume
The honest starting point is that you cannot instantly DM everyone on a real spike. That is a Meta ceiling no tool escapes. What actually helps:
- Keep the first DM short and conversational. Put the link in message two. First messages that lead with a link are more likely to get filtered into hidden message requests, so a simple opener lands with more people.
- Go back and sweep the post. Re-scan the existing comments and DM the ones who matched your keyword but never got a message, while they are still inside the 7-day window. This is where most of your "lost" people are actually recoverable.
The short version
The cap is real and shared by every comment-to-DM tool on the market. But your misses mostly are not permanent. If you sweep the post again within 7 days, you can recover the tail that the live sends missed.
One thing worth knowing
ManyChat cannot go back over comments it missed; its own community moderators say there is no retroactive option. ChatGenius has Rewind for exactly this: point it at the post and it DMs the people who matched your keyword but never got a message, as long as they are still inside the 7-day window. Each run sends up to 200, paced under Meta's hourly cap, so a big post takes a few runs. Rewind is on Creator and up, and Free gets one trial run. And when Meta rejects a single DM or public reply with a temporary error, ChatGenius keeps retrying it for up to 6 days instead of dropping it.
Start free Free plan, no card needed. Or see how Rewind works.Frequently asked questions
Meta caps comment private replies per account per hour (the documented ceiling is 750 per hour, and most tools throttle under that to stay ban-safe). On a 15,000-comment spike you blow past that limit, so in a tool that queues, the excess goes out as the rolling hour frees up rather than being dropped.
Yes, and it is a Meta platform limit, not a ManyChat-specific one. Every comment-to-DM tool shares the same per-account hourly ceiling, so none of them can instantly DM everyone on a true viral spike.
The initial private reply to a comment has a 7-day window. The 24-hour window applies to continuing a conversation after someone replies to you, which is a different thing. You have a full week to land the first DM.
Yes, as long as they are still inside the 7-day private-reply window. You re-scan the post and send the DM to anyone who matched but never received one. ManyChat is forward-only and cannot do this, but tools with a retroactive backfill can sweep the post and catch the tail.
Accept you cannot instant-DM everyone, keep the first DM a short conversational opener with the link in message two, and re-scan the post to recover missed commenters while you are still inside the 7-day window.