VAST Error 406: Mezzanine required but not provided

The environment required a mezzanine file, but the VAST response did not provide one. In operations, this usually shows up when the workflow depends on mezzanine availability for transcoding or ad-stitching preparation.

This is the kind of issue that is easiest to solve when the investigation starts from the right evidence path. VAST Inspector is usually the fastest first step because it confirms whether the response, wrapper chain, or media selection behaves the way the player expects.

This is especially relevant in ad-stitched or transcoding-heavy environments where the mezzanine file is operationally required, even if not always required by basic validation.

The most common causes are missing mezzanine asset in the VAST response, SSAI or publisher policy requiring mezzanine support, and creative packaging that omitted a high-quality source file. Teams often treat the visible error as the root problem, but in practice the real issue may sit earlier in the wrapper path, in the creative package, or in the environment assumptions around the request.

That is why it helps to compare a failing request against a known-good example. Once you know whether the difference is structural, timing-related, or environment-specific, escalation becomes much faster and cleaner.

VAST Inspector should be the first stop for this class of issue. From there, move into VAST Error Code Explainer to narrow the failure further.

A useful investigation should end with concrete evidence: the failing tag or asset, the exact point where the player behavior diverged, and the partner or configuration change most likely responsible. That turns a generic player code into an actionable support ticket or launch fix.

Confirm whether the execution environment requires mezzanine, then verify the response includes it and that trafficking understands the stitched workflow.