Hi Colin,
I’m on my phone since I often have other priorities when on my laptop.
I know that End Experiment code can conflict with the smooth exit of a PsychoPy experiment, so I would strongly recommend that you try a different approach and then ask for help with that.
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Is there a reason why you aren’t just using the Completed URL in Experiment Settings? If it needs to be dynamic then you could use CompletedURL / IncompleteURL - #23 by jon