Thank you for your post.
Can you confirm the URL that your are using to access the App Gallery? Is it appgallery.services.xerox.com or appgallery.external.xerox.com?
If the URL contains 'external.xerox.com', please clear your browsing history and try the appgallery.services.xerox.com URL. The .external.xerox.com URL should work, but it looks like there's an issue with the redirect currently. We are looking into this, but if you use the .services.xerox.com URL that should get you by the error.
On other item to check. Do you have more than one Extension installed? If you do, you will have trouble using the App Gallery. You can check this by looking in the upper right corner of your browser. You should only have one icon like this:
If there is more than one, remove any that are not labeled 'Xerox Device Connector' when you click on it.
Please let me know if this does not resolve the error for you and I will continue to investigate.