I've moved your question to the InDesign EPUB forum that was created recently.
If the support staff at Ingram Spark is not helpful, maybe you'll just have to deal with the eBook sellers yourself. If the file passes IDPF validation, and if it view correctly on the eBooks you want it on, then the problem is at their end, not yours.
Have you made any manual changes to the "content.opf" file in your epub?
No, I did not make such changes. I was able to successfully upload a
file by turning off the CSS output in the INDD document preferences.
it seems from the error that there's some invalid data has been entred in the metadata of the epub.
Have you placed or altered any metadata fields?
Try resetting your metadata content and try again.