SOLUTION FROM APPLE:
I've got a reply from Apple support as follows:
Follow this basic troubleshooting to attempt to solve it as this issue was previously reported and solved by our engineering team on August 8th.
Make sure you are using the latest version of your browser.
Clean the cache, cookies and history (all website data).
Get out of your browser completely.
Try again
I would also like to recommend that you try Safari, since our website is optimized for Safari.
If the error still appears, to better assist you, we need more information. Please provide the following:
• Steps to reproduce the issue
• Full-window screenshots or video illustrating the issue
• Username of each user experiencing the issue
• Web browsers that you were able to reproduce the issue in
• Web browser version numbers
• Apple ID of the In App Purchase
**Works for me! **