WebSession.finalize call to be successful while the underlying SOAP API call was not.
Therefore, your code should check that both the WebSession.finalize call and the API return within it returned a 200 for success.
As different API calls will use the same return codes to mean different things, please reference API name, return code, and return strings to get a complete error view and reference lists for each method in the Subscribe API Guide.
Parent topic:Working with HOA with Hosted Fields