Internal error when trying to run experiment in browser (Pavlovia) – unhandled error in Builder (v2025.2.4beta, macOS)

Hi everyone,

I’m encountering an internal PsychoPy error when trying to run my experiment in the browser (Pavlovia). I’ve attached a screenshot of the full traceback.

Environment:

  • PsychoPy version: v2025.2.4beta

  • macOS

  • Using Builder

Main issue:
I understand that linking to a Pavlovia Survey requires running the experiment in the browser (since surveys are online-only). However, my experiment cannot successfully run in browser mode. It crashes during the export/JS preparation stage with an “unhandled internal error.”

The experiment runs locally without issues, but browser run fails before launch.

Additional details:

  • The Pavlovia survey itself works fine when accessed directly via its URL.

  • When I include the Pavlovia Survey routine, browser run fails.

  • I also tried removing the Pavlovia Survey routine entirely and replacing it with a simple redirect to the survey URL, but browser run still fails.

  • I deleted and reinstalled PsychoPy, but the issue persists.

So the core problem seems to be that the experiment cannot be compiled/run online at all, which prevents me from linking to the Pavlovia Survey (since that requires browser execution).

My question:
Is linking to a Pavlovia Survey strictly dependent on successful browser/JS compilation? And could this be a bug related to the beta version (v2025.2.4beta)?

Any suggestions on what might cause browser export to fail like this would be greatly appreciated.

Thanks!

Your Builder view behind the error message shows you aren’t logged in, which is certainly one reason why you can’t sync.