Read channel reports to check that your products are properly configured at both the product creation level (products feed) and for updates (offers feed).
These reports list only items which were rejected by Zalando. For each product in error, Zalando specifies the reason for the rejection.
The errors are detailed in this Zalando documentation: Artikelstatus-Code-Definitions.
Note: If at some point an error was sent for a product and wasn't corrected, Zalando will keep sending this error in the report, even if the corresponding product is not sent anymore.
If a variation of the same product is incorrectly configured, all products linked together won't be published.