What is an API rate limit?

Each request an app makes, such as reading a comment, sending a DM or looking up a profile, counts against a budget. Services set budgets so one busy app can’t slow things down for everyone else, and so mass messaging stays expensive. Once an app runs out, its calls fail until enough time has passed.

• Windows: some limits reset at a fixed time, others count backwards from now. Meta counts its Instagram limit over a rolling 24 hours.
• Signals: many APIs answer an over-limit request with HTTP status 429, Too Many Requests. Meta’s Graph API says which limit was hit with an error code in the response.
• Warnings: Meta reports usage as it goes, in the X-App-Usage and X-Business-Use-Case-Usage response headers. The second includes estimated_time_to_regain_access, the minutes until a throttled account can call again.

Impressions here count how many times the account’s content was on someone’s screen in the last 24 hours, so a more visible account gets a bigger budget. Engaged users are the people a Page can currently message: a Page with 50 of them can make 200 × 50 = 10,000 Messenger calls in a day.

Say a fitness creator’s Reel offering a free training plan gets 2,000 “PLAN” comments in its first hour. At 750 private replies an hour, the last of them can’t be answered until the third hour: 2,000 ÷ 750 is about 2 hours 40 minutes of sending.

Nobody misses out, because a private reply can be sent up to 7 days after the comment. The cost is waiting: early commenters get their DM at once, later ones hours afterwards. DMFast stays under 700 private replies an hour per account to leave headroom and queues the rest, so the same 2,000 comments clear in just under 3 hours.

Tip: Only the first DM to each commenter counts against the hourly cap on private replies. Once someone answers it, the chat continues as ordinary messages, which Instagram limits per second rather than per hour.

• Spread calls out. Meta’s own advice is to space queries evenly instead of sending bursts.
• Stop when told. After a rate-limit error, the right move is to pause until access returns, not to retry in a tight loop that eats the budget faster.
• Queue the overflow. Comments that can’t be answered this hour wait in line and go out oldest first.
• Leave headroom below the cap, so retries and re-runs don’t push the account over.
• Don’t fetch what doesn’t change. A commenter’s username or a post’s caption doesn’t need looking up again for every message.