VAST error code
901 — General VPAID error
What the spec says
The VPAID unit failed to initialise or execute.
What actually causes it
- VPAID not supported in the environment at all — the normal case in CTV and most in-app SDKs.
- The VPAID JavaScript failing to load, or erroring once loaded.
- A handshake timeout between the unit and the player.
- Content Security Policy on the page blocking the script.
How to fix it
Treat VPAID as unsupported by default in 2026 and plan around it. Support has been withdrawn across most of the ecosystem in favour of SIMID for interactivity and Open Measurement for verification. If interactivity is not essential, serving a plain MP4 will materially improve delivery.
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.