we have a requirement to share product object with external users but due to security concerns we have to keep product object  sharing setting to private. and in community sharing setting product object is not visible 

The instructions state:

"The method must return the ID and Name for the requested record and all associated contacts with their ID and Name."

I am returning a List<sObject> where the first object is the Account and the remaining objects are the Contacts.

The error message is:

"Executing the 'AccountManager' method failed. Either the service isn't configured with the correct urlMapping, is not global, does not have the proper method name or does not return the requested account and all of its contacts."

I assume it is looking for a different structure to be returned by getAccount() besides List<sObject> but since Account doesn't have a field to store associated Contacts, I'm not sure what to return.

Anyone able to clarify for me what type & structure the return value should have?