Meta APIs limit replies to private messages:
Facebook and Instagram connected through Facebook: up to 7 days after sending
Instagram connected directly: up to 24 hours after sending
After that time, messages appear in the Inbox but you can't reply to them from Metricool. You'll need to reply directly from the social network's app.
There is no time limit for replying to comments on Facebook and Instagram.
Note: These time windows refer exclusively to the ability to reply. Deleting comments is not available from Metricool at any time.