Output path should be blank
In PsychoPy version 2020.1, the files needed for running an experiment online were created in a sub-folder of the experiment folder, usually called html, along with copies of any necessary resources (spreadsheets, media files, etc.).
Since version 2020.2.0 this has no longer been necessary, which saves on server space. More recent versions of PsychoPy will fail with resource errors if you try to use an output path.
Delete the contents of Experiment Settings / Online / Output path (probably html)
Delete the local folder created by the output path setting.
Resync with Pavlovia.
You may need to switch the experiment to inactive and then piloting/running again.