The type 'SoapHttpClientProtocol' is defined ... You must add a reference to assembly 'System.Web.Services, Version=2.0.0.0,'. in mvc core1.1

Question

Hi i use a web reference in my Project i use visual studio 2017 with mvc core 1.1 and code like this .

send.SendGroupSMSAsync("TextBoxSignature.Text", "TextBoxSMSNumber.Text", mobiles, _MSG, false, string.Empty,  successCount,  ReturnStr);

now i have this error

The type 'SoapHttpClientProtocol' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Web.Services, Version=2.0.0.0,'. in mvc core

in core 1.1 how can i add this?