SlingAgentImage requirements by platform
Every network decides for itself what it will accept as a post image, and they don't agree. The same file can sail through Facebook and be refused by Instagram in the very same batch. That isn't SlingAgent failing — it's two platforms applying two different rules to one picture.
This page is the reference for what each one takes.
| Platform | Accepted shape | Max file size | Recommended |
|---|---|---|---|
| 4:5 to 1.91:1 | 8 MB | 1080x1080 (square) | |
| Any shape | 4 MB | 1200x630 (landscape) or 1080x1080 | |
| Threads | Up to 10:1 | 8 MB | 1080x1080 |
| X | Any shape | 5 MB | 1200x675 (16:9) |
| Any shape | 10 MB | 1200x627 (landscape) | |
| Any shape | 20 MB | 1000x1500 (2:3 portrait) | |
| Bluesky | Any shape | 1 MB | 1200x675 |
| Mastodon | Any shape | Varies | 1200x630 |
| TikTok | Video only | Varies | 9:16 vertical video |
Accepted shape is the aspect ratio: width divided by height. 1:1 is a square, 1.91:1 is a wide landscape image, 4:5 is a tall portrait one. Where a platform is listed as Any shape, it has no published limit strict enough to reject a normal image — though very wide or very tall pictures still get cropped in previews.
Instagram is the strict one
Instagram is the only connection that routinely rejects images outright, and it's the one people hit. It accepts 4:5 to 1.91:1 and nothing outside that.
Two very common images fall outside it:
- Wide banners and logo lockups. A 3:1 header graphic is far wider than 1.91:1 and will be refused.
- Story-shaped images. A 9:16 vertical (1080x1920) is a Story or Reel format, not a feed format, and the feed will refuse it.
You shouldn't often get that far, though. When you upload an image, SlingAgent measures it and warns you straight away if a platform you're posting to won't take that shape — on the promo card, and in Share once as you tick and untick accounts. The upload still goes through: the warning tells you what will happen, it doesn't stop you.
If a post does go out and get refused, the promo shows Failed with an explanation naming the limit. Nothing is lost — fix the image and publish again.
Fixing a rejected image
Pad it, don't crop it. Cropping a wide logo to 1.91:1 slices off both ends. Instead, place the existing image centred on a 1080x1080 canvas filled with your background colour. The artwork survives intact and the shape becomes legal.
A square works on every network SlingAgent posts to, so when you only want to make one image, make it square.
You can also click Generate image on the promo to get a compliant one, or Upload a replacement — see Promo images.
File size
Bluesky has the tightest ceiling at roughly 1 MB, so a large PNG tends to fail there first while posting fine everywhere else. Saving as JPG instead of PNG usually solves it in one step.
Mastodon limits are set by your instance, not by Mastodon, so they vary; 8 MB is the common default. Your own uploads to SlingAgent are capped at 4 MB (PNG, JPG, or WebP).
TikTok is video-only
TikTok promos need a rendered video rather than an image — click Make video on the promo. See Short-form video.
If a post fails for a reason this page doesn't explain, the message on the promo comes straight from the platform that refused it. Platform policies covers removals and account limits, which are a separate matter from image formats.