Failure | ErrorCode:21916519
ShortMessage:Listing is missing required item specific(s): "Style".
LongMessage:Listing is missing required item specific(s): "Style". Please provide the required item specifics.
Style is one example, different item-specifics can take its place.
This is because the field "style" is a required item specific for that item to be listed on eBay and has not been added to the item specific set in the Settings > Channels > eBayMainOptions, please see below:
Select the style field and save settings and it will be added to the fields section shown in the image.