Hello Dwity,
What is the OData version of the external service ? V3 ?
Please try to consume V2 version of the service and check.
http://services.odata.org/V2/OData/OData.svc/Suppliers
http://services.odata.org/V2/OData/OData.svc/Categories
http://services.odata.org/V2/OData/OData.svc/Products
As far as i know V3 version of the service is still not supported.
Regards,
Ashwin