VAST-2.0-extensions-unknown-child
VAST-2.0-extensions-unknown-child
<Extensions> may only contain <Extension> elements
ErrorSchemaIAB VAST 2.0 §2VAST 2.0 and later (all versions)
Short answer
<Extensions> is a container for <Extension> elements only.
Why this matters in production
This rule is usually a delivery blocker. Many players, SDKs, and ad servers will discard the response or skip the affected creative once this condition is hit. Schema violations tend to create parser disagreement. One system may recover while another drops the tag entirely, which is why these bugs often show up as environment-specific fill loss. Affected scope: VAST 2.0 and later (all versions).
How to fix
Wrap the element inside an <Extension type="custom"> block inside <Extensions>.
Check your VAST tag for
VAST-2.0-extensions-unknown-child and other issues instantly.Validate a tag →Other Schema rules
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