VAST error code
201 — Video player expecting different linearity
What the spec says
The player expected a linear ad and received a non-linear one, or vice versa.
What actually causes it
- An overlay creative trafficked to an in-stream pre-roll slot.
- A linear video returned for a placement configured for overlays.
How to fix it
Check the linearity setting on the placement and the creative type being served. The two must agree; players do not adapt between them.
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.