using System;
using System.Linq;
using System.Text.RegularExpressions;

namespace ConsoleApp3
{
    class Program
    {
        static void Main(string[] args)
        {
            string text = "eCheck payment for ^1 received. Receipt Date: 04/30/2019 from BANK OF AMERICA N.A. Checking Account ending in 5565.";
            string pattern = @"eCheck payment for (\S+?) received. Receipt Date: (\b\S+?\b) from BANK OF AMERICA N.A. Checking Account ending in (\b\S+?\b).";


            var placeholders = Regex
                                .Matches(text, pattern)
                                .OfType<Match>()
                                .SelectMany(m => m.Groups.OfType<Group>().Skip(1).Select(g => g.Value));


            foreach (var variable in placeholders)
                Console.WriteLine(variable);

            /* OUTPUT

            ^1
            04 / 30 / 2019
            5565

             */
            Console.Read();
        }
    }
}