VAST-2.0-inline-unknown-child
VAST-2.0-inline-unknown-child
<InLine> contains an unrecognised child element
ErrorSchemaIAB VAST 2.0 §2.3VAST 2.0 and later (all versions)
Short answer
<InLine> has a defined set of child elements. Any element not in that set is a schema error and will be ignored by spec-compliant players.
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
Remove the unrecognised element from <InLine>, or wrap it in <Extensions><Extension type="custom">…</Extension></Extensions>.
Check your VAST tag for
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