C++ - Sended request is not reaching other computer

I am using libcurl with C++ to send an HTTP request to another host (my friend's computer) over the Internet. Now, the other end uses a Node.js script to receive and handle the request. I have tried the code (both C++ and Node) on my local network between my computers, and everything works just fine. This is the code, in case you wanna look at it:

CURL *handle;
string response;

curl_global_init(CURL_GLOBAL_WIN32);
handle = curl_easy_init();

curl_easy_setopt(handle, CURLOPT_URL, "10.10.10.10:7890"); //<= IP:PORT of the remote host
curl_easy_setopt(handle, CURLOPT_POSTFIELDS, "This is my POST request data!!");
curl_easy_setopt(handle, CURLOPT_WRITEFUNCTION, write_to_string);
curl_easy_setopt(handle, CURLOPT_WRITEDATA, &response);

curl_easy_perform(handle);

curl_easy_cleanup(handle);

and the Node.js code:

var http = require("http");
var server = http.createServer(function(request, response) {

    request.on('data', function(chunk) {

        console.log("We got a connection!");

        console.log("Received POST data:");
        console.log(chunk.toString());

    });

});

server.listen(7890);
console.log("Server is listening");

As I said, on my local network it works very well, but why it doesn't my friend receive the request? I noticed that my code (C++ part) takes some time, before closing, as if it was trying to connect. Is this some kind of firewall problem? We have tried disabling it, but nothing changed. We are almost total noobs with networking, and we're trying to get into it.

If anybody could help us, thanks in advance!