Only Google namespaces are supported in XML feeds.
On this page
Reason why the issue is happening
You've defined and used a namespace that's not supported in your XML. Only the Google base namespaces 'http://base.google.com/ns/1.0' and 'http://base.google.com/cns/1.0' for custom attributes are supported.
How to fix the issue
Remove any other namespaces and the attributes referencing those namespaces from your XML file.
Next steps
After making the requested changes, check that you've fixed the issue by making sure that it's no longer listed on the 'Needs attention' page.
Bear in mind: It may take some time for your change to be reflected on the 'Needs attention' page.
Learn more about product data specifications.