C# variables in Sequence diagram

Question

I am playing with sequence diagram. And main question is how to draw properly on sequence diagram interaction with variable. How to draw

1) When MakePayment aggregates person

insurance.MakePayment(person.FirstName, person.SecondName, 20);

2) Variable assignment

internalVariable = SecondName;

I am not sure that I draw right sequence.

namespace Example
{
    public class Person
    {
        public string FirstName { get; set; }

        public string SecondName { get; set; }

        public string Salary { get; set; }
    }

    public class Insurance
    {
        private readonly Bank bank;

        public Insurance()
        {
            bank = new Bank();
        }

        public bool MakePayment(string FirstName, string SecondName, int value)
        {
            if (bank.GetBalance(FirstName, SecondName) > value)
            {

            }
            return true;
        }
    }

    public class Bank
    {
        private string SomeVariable { get; set; }

        private string internalVariable;

        public Bank()
        {

        }

        public decimal GetBalance(string FirstName, string SecondName)
        {
            SomeVariable = FirstName;
            internalVariable = SecondName;
            return 320;
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Person person = new Person();
            person.FirstName = "FirstName";
            person.SecondName = "SecondName";
            Insurance insurance = new Insurance();
            insurance.MakePayment(person.FirstName, person.SecondName, 20);
            PrintResult(person.FirstName);
        }

        public static void PrintResult(string firstName)
        {
            Console.WriteLine(firstName);
        }
    }
}

Answer 1

I think you're putting to much information in your diagram. You can of course, but this kind of diagrams are usually used to show, as simply as possible, the interactions between actors in a use case.

In this case, the actors would be:

1. The User clicking on the Make payment button.
2. The Insured person receiving the money from the insurer.
3. The Insurer.
4. The Bank.

The messages exchanged would be:

1. User to Insurer: Make Payment (Parameter=Insured)
2. Insurer to bank: Get Balance (Parameter=Account)
3. Bank to Insurer: Done (Parameter=Balance)
4. Insurer to bank: Transfer Money (Parameters=Amount, Insurer Account, Insured Account)
5. Bank to Insurer: Done (Parameter=Transaction code)
6. Insurer to User: Done (Parameter=Transaction code)

You could also show on the same diagram the interaction resulting for insufficient funds, or create a new use case for this.

Object creation should not be shown, unless it is crucial (if you want to show how an object factory create an object, for example).