A CORS error indicates a cross-origin request problem. Are you on non-WWW for the site, but the upload request is going to WWW or vice-versa? What I've seen cause this is not enforcing WWW or non-WWW at a server config level but having the EE config set to one or the other. So, if you try to make a post request, and EE is set to use www.site.com as the URL for that post request, but your on site.com with no WWW, you could get a CORS error.
Replied 2/25/2020 10:47 PM
Right!!!!! Sleep deprivation makes the obvious so blurred at times :p