Error Code 21920061
… is not allowed as a variation specific.
This error only occurs in variation listings. If a parent receives this error, it means that the option mapping of that variation group has not been completed.
To fix this error, please follow the steps below.
1- Go to eBay Channel > Channel > Channel Products > Find related parent and click the Edit button under the Actions tab.
2- Product Editor will open. Go to Option Mapping tab.
3- Select the necessary fields from the drop-down list and remember to click on the Save&Close button.
4- Select the related parent and its children, force product data update, and Sync the channel.