The account type, which is nearly always the answer
If a scheduler cannot post for you, the first thing to check is not the scheduler. Instagram’s publishing API accepts Professional accounts only. A Personal account cannot be published to by any third-party tool, and no amount of reconnecting will change that.
Switching is free and takes about a minute: Instagram → Settings → Account type and tools → Switch to professional account. Your profile, followers and posts are untouched.
Professional gets you photos and carousels. Business is the one that gets you Reels.
That second sentence is the step almost every guide leaves out. Instagram publishes video from Business accounts only, and IGTV was retired, so every video is now a Reel. A Creator account will publish your photos happily and then refuse the first Reel you schedule — usually with an error that does not mention the account type at all.
What Instagram accepts, exactly
These are hard failures, not warnings. A post that breaks any of them is rejected rather than adjusted.
- Images must be JPEG. A PNG is refused. This catches almost everybody once, because a PNG is obviously a photo.
- Image aspect between 4:5 and 1.91:1. Images only — video is 9:16, and applying the image range to it would reject every real Reel.
- Carousels cap at 10. The app allows twenty; the API does not.
- Captions cap at 2,200 characters, 30 hashtags and 20 @-mentions — each its own hard failure.
- Video up to 15 minutes, as MP4 or MOV.
- A rolling daily cap per account. Meta’s documentation gives two different numbers, so the only reliable answer is to ask the account.
Why you find this out at 9am
None of the above is checked when you write the post. It is checked when the post is sent — which, for anything scheduled, is the moment it was meant to go live and the moment you are least able to do anything about it. A PNG that has been sitting in a calendar for three weeks fails at nine on Tuesday morning.
That is the argument for checking at planning time instead. Ninecast runs every rule on this page against each row while you are still looking at the planner, so a post that cannot publish says so in the week you wrote it. You can also check a single image against every Instagram crop with the free crop checker and the caption checker, without an account.
If a scheduled post did not go out
Account type and file rules are the common causes, but not the only ones. Why a planner stops posting works through the rest in the order worth checking them — expired connections, missing dates, media that never finished uploading.
Questions that follow
Why can’t an app post to my Instagram automatically?
Almost always the account type. Instagram’s publishing API only accepts Professional accounts — Business or Creator. A Personal account cannot be published to by any third-party tool, whichever one you use. Switching is free, takes a minute in Instagram’s settings, and changes nothing about how your profile looks.
Is a Creator account enough?
For photos and carousels, yes. Not for video. Instagram only publishes video from Business accounts, and since IGTV was retired every video is a Reel — so a Creator account cannot auto-publish Reels at all. This is the step most guides leave out, and it is the one people hit after they have already switched once.
What is the difference between auto-publishing and notification publishing?
Auto-publishing sends the post at its scheduled time with nothing for you to do. Notification publishing sends your phone a reminder and you finish the post by hand. Tools that support Personal accounts are doing the second one, which is a reminder rather than a scheduler.
What file types does Instagram accept through the API?
JPEG for images. A PNG is rejected outright, which surprises most people the first time — it is a photo, so it feels like it should work. Video must be MP4 or MOV.
How many images can be in a carousel?
Ten through the API, even though the Instagram app itself allows twenty. A carousel of fifteen planned in an app will not publish through any scheduler.
What are the caption limits?
2,200 characters, at most 30 hashtags and at most 20 @-mentions. Each of those is a hard failure rather than a truncation — go over on any one and the post is rejected, not shortened.
Do image aspect ratios matter?
For images, yes: between 4:5 and 1.91:1. That range does not apply to video, which is why applying it to a Reel — 9:16 — would reject every legitimate one. You can check any image against every Instagram crop with our free crop checker.
Is there a limit on how many posts a day?
Yes, a rolling 24-hour cap per account. Meta’s own documentation contradicts itself on the exact number, so the honest answer is to read it from the account rather than quote a figure — which is what we do before publishing.
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