If your products show an eBay validation error like this:
"ebay validation error: UPC should only contain digits" and it is followed by scientific notation.
It means that an update has gone wrong somewhere, most likely while updating Product Identifiers in your store via copy/paste from Microsoft Excel which changed number field for this Product identifier e.g. UPC to this "9.111E+12".
This eBay validation error can also occur if your UPC contains non numeric characters, e.g. 14500-459-1111, these should be removed.
You can also get this error with UPC's containing letters, eg when the SKU or the MPN has been placed in the UPC field, again either remove UPC or update it with the correct one.
More information about UPC can be found here: https://en.wikipedia.org/wiki/Universal_Product_Code
Please check this data on your store and correct it, once done, go to the dashboard and click "Sync now" to refresh the data.
For more information about Excel issue see this article. http://superuser.com/questions/413226/why-does-excel-treat-long-numeric-strings-as-scientific-notation-even-after-chan
You can validate your UPC here https://www.upcdatabase.com
You can check GTIN existence here https://gepir.gs1.org/index.php/search-by-gtin
Listings having an eBay validation error will not be updated or listed on eBay until the error is resolved.