LINE error 400: The image size is not allowed for richmenu

Uploading a rich menu image (POST https://api-data.line.me/v2/bot/richmenu/{richMenuId}/content) failed because the image doesn't meet LINE's requirements. The error table says "The image doesn't meet the requirements," and despite the message mentioning size, the requirements cover more than dimensions:

Image format JPEG or PNG; image width 800 to 2500 pixels; image height 250 pixels or more; aspect ratio (width / height) 1.45 or more; maximum file size 1 MB. Any one of these failing produces the same message. A phone screenshot fails the aspect ratio, a high-quality PNG export often fails the 1 MB cap, and a 3000-pixel design file fails the width limit.

One more rule interacts with this. The image should match the size you declared in the rich menu object, because the tap areas (bounds) are laid out in that coordinate space. Separately, if the Content-Type header isn't image/jpeg or image/png, you get a 415 rather than this 400 (see 415 Unsupported Media Type).

// If you specify an image that doesn't meet the requirements (400 Bad Request)
{
  "message": "The image size is not allowed for richmenu"
}

Validate the image in your build or admin tool before calling the API: format, width 800-2500, height at least 250, ratio at least 1.45, and file size under 1 MB. Store a known-good template at the exact rich menu size your designers use. The full set of rich menu numbers is collected in rich menu limits.