404 error using Wakecarter's tool to assign consecutive participant id's

I’m trying to set up my Pavlovia study in Prolific and have implemented counterbalancing based on Wakecarter’s page which assigns consecutive participant numbers and then redirects to alternating URLS.

However when I try to visit the page ‘https://moryscarter.com/vespr/pavlovia.php?folder=EOResearch&experiment=bfi_filler_exp_final’, with or without a slash at the end, I get a 404 not found error. Interesting the url shows participant= 6, but I cannot access the page.

I have also tried with the prolific URL Parameters at the end, e.g ‘&id={{%PROLIFIC_PID%}}’ but that doesn’t change anything.

Any insight would be greatly appreciated!


What is the URL for your experiment?


both give 404 errors

which is why my tool is failing to launch them.

Hi, so sorry, I finally realised it’s an issue of an errant capitalisation of the R in research ‘https://moryscarter.com/vespr/pavlovia.php?folder=EOresearch&experiment=bfi_filler_exp_final/’ works just fine now. Thanks so much!

Hi @wakecarter,
Thanks so much for this wonderful resource! We’re also trying to use your tool and we’ve run into a similar error:
The original research URL is part1V2_final [PsychoPy], which works fine,
but when we try running https://moryscarter.com/vespr/pavlovia.php?folder=eldarlabccl&experiment=combined_part1v2&id=c&researcher=d, we get a “404 page not found error”. Do you know what did we do wrong?

When the tool was written, Pavlovia experiments ran from an html sub folder. To signal that you are running from the experiment folder itself (the default since 2021.2) you need to add a / to the end of the experiment folder name.

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Hi @wakecarter thanks so much for this tool.

We are attempting to use your code to set consecutive ids for session


which in theory works and takes us to the right link etc… however, when we look at the data session is still 1 or 2.

more generally, we are trying to assign consecutive participant numbers as well as their prolific ID (since its a multisession study) - so if there is a better way to do that please let us know.

Thanks so much

You seem to be including id and researcher without any content (apart from the example letters) and then you are sending {{%STUDY_ID%}} as PROLIFIC_PID which won’t get passed through. Try


Even though it seems to work in testing (the link shows ascending sessions)- our data file keeps returning session=1 for all participants. Any idea what could be going wrong?