Hey mate,
I had this issue a couple of weeks ago when the URLs are returning an issue about authentication.
The base URL that you use needs to be modified. I documented this in the following post oData SuccessFactors Authentication (401 error)
For your URL, I think you need to use https://api8.successfactors.com/odata/v2/$metadata or apisalesdemo8.successfactors.com/odata/v2/$metadata or similar.
I am using the salesdemo4 system and it took me a few tries to find the correct URL.
You're getting there 
Good luck
Greg