Just want to share.
If you try to upload screenshots or other resouces to https://appstoreconnect.apple.com/ and constantly get "your file could not be uploaded".
If your browser's console report like this.
> vendor.84585ca92f.js:13 OPTIONS https://du-itc.itunes.apple.com/upload/image 503 (Service Unavailable)
> versioninfo:1 Failed to load https://du-itc.itunes.apple.com/upload/image: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'https://appstoreconnect.apple.com' is therefore not allowed access. The response had HTTP status code 503.
> ssController:943 ERROR uploading image to DU: null
Use
https://itunesconnect.apple.com/
instead of
https://appstoreconnect.apple.com/
Apple doesn't seems to configure CORS settings of https://du-itc.itunes.apple.com/ to accept
