Instagram error 100: Attachment size exceeds allowable limit
Last verified against Meta for Developers - Messenger Platform error codes
Attachment size exceeds allowable limitWhat error 100 means
Subcode 2018109 is the media size ceiling: the file you attached (by URL or upload) is bigger than the platform allows for its type. For Instagram messaging the documented maxima are 8 MB for images and 25 MB for audio and video - small numbers by modern phone-camera standards, which is why this error is so common in integrations that forward user-generated or CMS-sourced media untouched.
The error is deterministic per file: the same asset fails every time, for every recipient, until it is compressed or replaced. That distinguishes it from the fetch problems under 2018008, which depend on hosting conditions. Note the interplay of dimensions and size for images: a 12-megapixel photo saved as PNG easily breaches 8 MB where a quality-85 JPEG of the same photo would not.
Why it happens
- Original-resolution photos (often 5-20 MB) forwarded directly from uploads or a DAM/CMS.
- PNG used for photographic content, inflating files past 8 MB.
- Video clips exported at high bitrate exceeding 25 MB even at short durations.
- Audio files in uncompressed formats (wav) breaching 25 MB for longer recordings.
How to fix Instagram error 100
- 1Compress before sending: re-encode images as JPEG under 8 MB, and transcode audio/video under 25 MB.
- 2Add an asset-size gate in the send path that rejects or auto-compresses oversized files before the API sees them.
- 3For video, prefer H.264 MP4 at a bitrate that fits the clip length under 25 MB, or host the full-quality version behind a link instead.
- 4Verify the actual bytes served at the URL (after any CDN transforms), not the size of the source file.
How to stop it recurring
Run every outbound asset through a normalization step - format, dimensions, and size - so the API only ever sees compliant files. Cache the normalized rendition and reuse its attachment ID for repeated sends. The full media matrix (formats and sizes per type, including the route differences for gif and pdf) is tabulated in the limits reference; fetch-side failures are 2018008.
Official reference: Meta for Developers - Messenger Platform error codes. See all Instagram error codes or the Instagram limits and quotas.
Related codes
Error 100 - quick answers
What does Instagram error 100 mean?
Subcode 2018109 is the media size ceiling: the file you attached (by URL or upload) is bigger than the platform allows for its type. For Instagram messaging the documented maxima are 8 MB for images and 25 MB for audio and video - small numbers by modern phone-camera standards, which is why this error is so common in integrations that forward user-generated or CMS-sourced media untouched.
How do I fix Instagram error 100?
1. Compress before sending: re-encode images as JPEG under 8 MB, and transcode audio/video under 25 MB. 2. Add an asset-size gate in the send path that rejects or auto-compresses oversized files before the API sees them. 3. For video, prefer H.264 MP4 at a bitrate that fits the clip length under 25 MB, or host the full-quality version behind a link instead. 4. Verify the actual bytes served at the URL (after any CDN transforms), not the size of the source file.
Stop debugging Instagram by hand
Connect the channel through Conferbot: tokens, webhooks and retries are handled, failures show as readable status.