Измените свой код следующим образом:
public string Insert_Users(AspNetUserModel aspNetUser)
{
if (aspNetUser != null)
{
AspNetUser model = new AspNetUser();
model.Email = aspNetUser.Email;
model.PhoneNumber = aspNetUser.PhoneNumber;
model.UserName = aspNetUser.UserName;
{
db.AspNetUsers.Add(model);
db.SaveChanges();
return "User Added Successfully";
}
}
else
{
return "User Not Inserted! Try Again";
}
}
Добавить модель
public class AspNetUserModel
{
public string Email {get;set;} //SET Your DataType
public string UserName {get;set;} //SET Your DataType
public int PhoneNumber {get;set;} //SET Your DataType
}