VAST error code

102 — VAST version not supported

What the spec says

The player understood the document but does not support the VAST version it declares.

What actually causes it

A VAST 4.x tag served to a player that only implements 2.0 or 3.0 — still common in older CTV and in-app SDKs.
A version attribute that is missing or contains a value that is not a published VAST version.
An ad server configured to emit the newest version by default without checking what the inventory supports.

How to fix it

Check what version the receiving player actually implements and serve accordingly. Most ad servers can be configured to emit a lower version. VAST is broadly backwards compatible, so serving 2.0 or 3.0 to a mixed estate is usually safer than serving 4.x everywhere.

To see whether a tag would hit this before it runs, paste it into the VAST validator. It reads the XML and reports the conditions that map to this code.

Related codes

Code definitions from the IAB Tech Lab VAST 4.3 specification. Causes and fixes are practitioner guidance, last verified July 2026.