HeyGen download_failed error: URL rules vs Sume's media errors

HeyGen's Usage Limits page says invalid resources passed to POST /v3/videos cause render failures with download_failed: the URL must be publicly accessible, the file extension must match the real format, and the file must not be corrupted. Sume rejects bad media with image_not_fetchable or input_media_unreachable, and requires fetchable public HTTPS URLs.

What makes a HeyGen URL fail with download_failed?

Three requirements, from the page read 2026-10-01: resource URLs are publicly accessible with no authentication, the extension matches the actual file format, and the file is not corrupted or malformed. The same section lists size limits per type: video 100 MB, image 50 MB, audio 50 MB.

What makes a Sume media URL fail?

The media inputs page says input image and video URLs must be fetchable public HTTPS URLs, and that localhost, private-network URLs, non-HTTPS URLs, signed or private URLs, and mismatched content types are rejected before generation submission. The errors page lists image_not_fetchable, input_media_unreachable and storage configuration errors as "Sume could not fetch or mirror media safely".

How do the checks line up?

How do I fix an unreachable media URL?

Open the URL in a clean session with no cookies, confirm it is HTTPS and returns the real file type, then retry. On Sume, the docs say to check that input media is a public HTTPS image URL, then retry or contact support with the request_id from the error envelope. For how retries interact with idempotency keys, see HeyGen idempotency vs Sume 409.