Find the answer to your question
I have set my shipping service to FreightShipping, which I got from GeteBayDetails. Then why am I getting the following error in my AddItem request?
<ShortMessage>Shipping service is not available.</ShortMessage>
<LongMessage>Shipping service Freight Shipping(16) is not available.</LongMessage>
To find out the valid Shipping Services that can be used, you need to make a call to GeteBayDetails. If the Shipping Service is valid for the selling flow, the ShippingServiceDetails container has the field ValidForSellingFlow as true. If the field is not returned, you cannot use the service for listing an item in the AddItem call.
The ShippingServiceDetails container for each service has many useful fields such as DimensionsRequired, ExpeditedService, InternationalService etc. which will help you determine how to use the service.
GeteBayDetails Call Reference