Same Project at Different URLs give different results

At

https://fastpalette.studio/ my project works fine

but at

https://www.fastpalette.studio/

I get the error (and thus total project malfunction):

Popups, event 27: TypeError: Cannot read properties of null (reading '_PostToDOMMaybeSync')

Line 27 is when I do a document.getElementById. At the point this is done I know the html exists(with the id) becasue I already did an Ajax request for the project file. So why the error on the url with www and not on the url without the www?

Cheers

Both seem to be working fine on my end. Btw I would recommend to redirect the domain to either of them in general (either with or without www)