using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var array = new ErrorList[]

        {       

            new ErrorList

            {

                ErrorCode = "1234",

                ErrorMessage = "Help"

            },

            new ErrorList

            {

                ErrorCode = "1235",

                ErrorMessage = "Help again"

            },

        };

        string errors = string.Join(',', array.Select(a => $"{a.ErrorCode}:{a.ErrorMessage}"));

        Console.WriteLine($"Error during response: {errors}");

    }

}

​

public class ErrorList

{

    public string ErrorCode {get;set;}

    public string ErrorMessage {get;set;}

}