VAST Error 502: Unable to fetch NonLinear resource
The overlay's image/iframe/HTML resource couldn't be downloaded — the non-linear equivalent of a 401.
The unit was accepted, but fetching its StaticResource, IFrameResource, or HTMLResource failed — dead URL, blocked host, or timeout. Same failure classes as media-file 401/402, applied to the overlay asset.
Why error 502 happens
Dead or moved asset URL
The image or HTML resource 404s — expired campaign assets are the usual culprit.
Blocked by the environment
Ad blockers and privacy tools block overlay resources aggressively, especially iframe-based ones.
Mixed content
An HTTP resource on an HTTPS page is silently blocked by the browser.
How to fix VAST error 502
- 1
Fetch the resource URL directly
curl it: the status code separates missing (404) from blocked (403) from slow (timeout).
- 2
Serve everything over HTTPS from a CDN
Eliminates mixed-content blocks and most latency failures in one move.
Seeing error 502 on a live tag?
Paste the tag URL or XML — the validator resolves the full wrapper chain, validates the schema, downloads every media file, and shows exactly which stage fails.
Validate your VAST tagVAST error 502 — frequently asked questions
Why do overlays fail to load more often than video files?+
Overlay resources look like display ads to blockers, and iframe/HTML resources trigger stricter browser security rules than plain video files do.