Authenticated assets are not accessed using token authentication

the following code is not working in cloudinary nuget package version -- 1.21.0. I am using .net core
AuthToken t = new AuthToken("MyKey").Expiration(1514764800);
string url = cloudinary.Api.Url
.AuthToken(t)
.Signed(true)
.Type("authenticated")
.BuildVideoTag("dog.mp4");

Type("authenticated") is not found in above code.

I am following https://cloudinary.com/documentation/control_access_to_media#delivering_token_based_authenticated_media_assets tutorial

Please also provide any sample for token based authentiv=cation .net core