Redirecting process's output isn't working C#

Question

I need to send an input from a C# program to another program and capture its process's output every time after the input is sent

Here I wrote a C program to be used as a process in C# program. The program will receive an input and print back the same string

#include <stdio.h>
#include <stdbool.h>
int main(){

    while(true){
        char buff[1000];
        scanf(" %[^\n]s", buff);
        printf("\nechoed : %s\n",buff);
      }
    
}

This is my C# program that will send input and receive output to and from my C program (I am starting the process in another thread so process.WaitForExit() will not block the main thread)

using System;
using System.Diagnostics;
using System.IO;
using System.Threading;
namespace MinExample
{
    internal class Program
    {
        static StreamWriter processStreamWriter;
        static string filePath = @"my_program.exe";
        private static void MyProcOutputHandler(object sendingProcess,
            DataReceivedEventArgs outLine)
        {
            if (!String.IsNullOrEmpty(outLine.Data))
            {
                Console.WriteLine("Data : " + outLine.Data);
            }
        }
        //this doesn't works
        static void StartProcessWithOutputRedirection()
        {
            ProcessStartInfo startInfo = new ProcessStartInfo();
            startInfo.CreateNoWindow = false;
            startInfo.UseShellExecute = false;
            startInfo.FileName = filePath;
            startInfo.WindowStyle = ProcessWindowStyle.Hidden;
            //standard input out redirection
            startInfo.RedirectStandardOutput = true;//redirect output
            startInfo.RedirectStandardError = true;//redirect output
            startInfo.RedirectStandardInput = true;

            try
            {
                //Initialize process and register callback
                Process process = new Process();
                process.StartInfo = startInfo;
                process.OutputDataReceived += new DataReceivedEventHandler(MyProcOutputHandler);
                process.ErrorDataReceived += new DataReceivedEventHandler(MyProcOutputHandler);
                //
                process.Start();
                //initialize stream writer so that the process can receive incoming input
                processStreamWriter = process.StandardInput;

                process.BeginOutputReadLine();
                process.BeginErrorReadLine();

                process.WaitForExit();

            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
        }
        //this works
        static void StartProcessNoOutputRedirection()
        {
            ProcessStartInfo startInfo = new ProcessStartInfo();
            startInfo.CreateNoWindow = false;
            startInfo.UseShellExecute = false;
            startInfo.FileName = filePath;
            startInfo.WindowStyle = ProcessWindowStyle.Hidden;
            //standard input out redirection
            startInfo.RedirectStandardOutput = false;
            startInfo.RedirectStandardInput = true;
           
            try
            {
                //Initialize process and set property
                Process process = new Process();
                process.StartInfo = startInfo;
                //
                process.Start();
                //initialize stream writer so that the process can receive incoming input
                processStreamWriter = process.StandardInput;
                process.WaitForExit();

            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
        }
        static void Main(string[] args)
        {
            /*
                using StartProcessNoOutputRedirection works but using StartProcessWithOutputRedirection doesn't
             */
            ThreadStart ths = new ThreadStart(StartProcessWithOutputRedirection);
            Thread th = new Thread(ths);
            th.Start();

            while (true)
            {
                Console.Write("Input :");
                string input = Console.ReadLine() ?? "";
                processStreamWriter.WriteLine(input);
            }
        }
    }
}

It will print the output each time the process receives an output when I don't redirect the output at all

However when I tried to redirect the output, the Process.OutputDataReceived event isn't being called back. I have searched another post and have tried to use process.BeginOutputReadLine(); after process.Start but it hasn't solved my issue

Any advice?