VAST error code
203 — Video player expecting different size
What the spec says
The dimensions of the creative do not match what the player expected for the slot.
What actually causes it
- MediaFile width and height attributes that do not match any size the placement accepts.
- A vertical creative delivered into a landscape player, or the reverse.
- Missing width and height attributes, leaving the player unable to confirm a match.
How to fix it
Confirm the MediaFile dimensions against the sizes the placement accepts, and make sure every MediaFile declares width and height. Offering several renditions at different sizes is the usual way to avoid this.
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.