You have sent products to eBay and they have gone into Fix Required. The accompanying error message says “Parent product must first be listed”.
You need to list a parent product in order to also list the child items. Only child items get this error in ChannelUnity.
Locate the parent for the item with the error in ChannelUnity; it will also be in the Fix Required section, but it will show a different error message. Resolve the error shown in this message and reupload – if you can successfully list the parent, then the child will go across as well.