Explanation: eBay API refused listing because one of eBay carriers you selected is not valid. Carrier list provided by eBay contains invalid carriers ! This is due to the fact that carrier validity depends on many parameters, including eBay account, product, payment, etc… When configuring eBay module, you have chosen an invalid carrier in your context.
Solution: You have to change invalid carrier in module configuration, and choose another carrier.
1 – Identify carrier
2 – Click to change carrier
3 – Click “Save”, then launch a new synchronization.