So we're trying to change the shipping option in our listings, and we're using a GetItem call and doing a search and replace for "UPSGround" and replacing it with "FedExGround". If we then send a reviseitem call (sending just the ShippingDetails block), we're getting an "Input data for tag is invalid or missing. Please check API documentation." error. If I comment out the line of code that changes the service type, it works fine. I've already confirmed that I am using the correct value for FedEx ground. Any ideas?