Full Error Message:
SKU does not match eBay Custom Label
The value (usually SKU) you are sending across for the Custom Label on eBay doesn”t match what is already on eBay for this item.
Error: SKUs do not match for ManageBySKU item specified by ItemID
ChannelUnity it trying to update an existing eBay listing but the SKU in the eBay custom label field does not match the SKU from ChannelUnity/Online Store.
Either update the eBay custom label field to match ChannelUnity/Online Store SKU or visa-versa
Delete and purge the listing in ChannelUnity which will send a delete request to eBay to remove the listing, wait 20 minutes, and then upload the product to create a new listing on eBay (note: the old listing will be deleted from eBay with all it’s history).