How do I post data using HttpSendRequest to a local server?

#define _WIN32_WINNT 0x600

#include <stdio.h>
#include <wininet.h>

#define BUFLEN 200

static const char *acceptTypes[] = {"application/x-www-form-urlencoded", NULL};
static const char *postData = "teststr=Hello+world&testval=42";

int main()
{
	HINTERNET hSession, hConnect, hFile;
	
	if( ( hSession = InternetOpen(
		"myapp",
		INTERNET_OPEN_TYPE_PRECONFIG,
		NULL,
		NULL,
		0
	) ) == NULL )
	{
		printf("Couldn't start session. Error %ld\n", GetLastError());
		exit(1);
	}
	printf("Session started\n");
	
	if( ( hConnect = InternetConnect(
		hSession,
		"localhost",
		INTERNET_DEFAULT_HTTP_PORT,
		NULL,
		NULL,
		INTERNET_SERVICE_HTTP,
		0,
		0
	) ) == NULL )
	{
		printf("Unable to connect to server. Error %ld\n", GetLastError());
		exit(1);
	}
	printf("Connected to server\n");
	
	if( ( hFile = HttpOpenRequest(
		hConnect,
		"POST",
		"/test/index.php",
		NULL,
		NULL,
		acceptTypes,
		INTERNET_FLAG_RELOAD,
		0
	) ) == NULL )
	{
		printf("Unable to open request. Error %ld\n", GetLastError());
		exit(1);
	}
	printf("Opening request..Opened\n");
	
	unsigned long dataLen = strlen(postData)+1;
	bool res = HttpSendRequest(
		hFile,
		NULL,
		0,
		(char*)postData,
		dataLen
	);
	if( !res )
	{
		printf("Unable to send request. Error %ld\n", GetLastError());
		exit(1);
	}
	printf("Request sent\n");
	
	return 0;
}

<?php if( isset($_POST['teststr']) ) echo $_POST['teststr']; ?>