VAST-4.0-category-authority
<Category> missing required authority attribute
Short answer
In VAST 4.0+, the <Category> element requires an authority attribute that names the taxonomy used (e.g., a URL pointing to the IAB content category list). Without it the category value cannot be interpreted.
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. Required-field failures usually stop validation early because the platform cannot determine the basic shape of the ad, the creative metadata, or the mandatory tracking payload. Affected scope: VAST 4.0, 4.1, 4.2, and 4.3.
How to fix
Add authority="https://iabtechlab.com/IAB_Tech_Lab_Content_Taxonomy" (or the relevant taxonomy URL) to <Category>.
Invalid
<Category>IAB1</Category>Valid
<Category authority="https://iabtechlab.com/IAB_Tech_Lab_Content_Taxonomy">IAB1</Category>VAST-4.0-category-authority and other issues instantly.Validate a tag →