VAST error codes / Linear and media errors
VAST error 406: Mezzanine required but missing
Short answer: A mezzanine file was required for SSAI but not provided. Introduced in VAST 4.1.
Debug this tag now
If you only have a live URL, test it first. If the failure is in the wrapper chain, inspect each hop. Validate resolved XML when you already have the response.
What your player reported
406· Mezzanine was required but not provided. Ad not served.
Wording from the IAB VAST 4.3 specification error table. Players may shorten or reformat it, but the code is the same.
What it means
Server-side ad insertion needed a high-quality mezzanine source to transcode, and the ad did not include one.
Common causes
- `<Mezzanine>` omitted where the SSAI pipeline requires it
How to fix it
Provide a `<Mezzanine>` that meets the platform's spec. 411 covers a mezzanine that is present but invalid.
VAST error codes are runtime buckets emitted by the player. They tell you where the failure happened, not which line of XML caused it. Paste the raw tag into the validator to map this code onto the exact element and rule.
Related vastlint rules
- VAST-4.1-mezzanine-type: <Mezzanine> missing required type attribute
- VAST-4.1-mezzanine-delivery: <Mezzanine> missing required delivery attribute
Related error codes
Debug this tag now
Validate the XML, follow the wrapper chain, or check it in CI before launch:
# CLI: exits non-zero on errors, ideal for pipelines
vastlint check creative.xml