Ok, This is for Salesforce generated CSR and signed by Public CA.
The certificate which I got from Pulic CA , I uploaded it to salesforce and passed all the stuff to third Party servers but they say that this certificate cannot be installed as it does not contain Keys, Now we also cannot provide them Keys sa sdc does not expose keys, So how this approach works actually? , Do we need to get it signed by Private CA authority? This should not be actually? There should be some standard way?