VAST error code
402 — Timeout of media file URI
What the spec says
The media file began loading but did not arrive within the player's timeout.
What actually causes it
- A file too large for the connection — a high-bitrate rendition on mobile is the classic case.
- A slow or poorly distributed CDN.
- Only one rendition offered, so the player has no lighter option to fall back to.
How to fix it
Offer several renditions at different bitrates so the player can choose one appropriate to the connection. A single 4 Mbps file is the most common cause of 402 on mobile inventory.
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Related codes
Code definitions from the IAB Tech Lab VAST 4.3 specification. Causes and fixes are practitioner guidance, last verified July 2026.