The MyOwnFreeHost API doesn't use any error codes, and will always return a 200 HTTP code. This is less than ideal, but it is what it is.
To do proper error handling, you would have to get the text inside the
<status></status> tags to get the status of your request (either
1). Or, if you use the
getdomainuser.php endpoints, you will see that it just returns
null instead of the list/array it usually gives.