Unable to Serve Multiple HTML Files Sequentially in Node.js HTTP Server

I’m running a Node.js HTTP server that is supposed to serve a HTML file if the user can login. However, I am experiencing issues where the server fails to send the HTML file as response. Here is the relevant (shortend) code snippet:

http.createServer((req,res) =>{
    // Get called over <a> tag
    if (req.url === "/login" && req.method === "GET"){
        res.writeHead(200, {'Content-Type': `text/html` });
        fs.createReadStream("./public/html/login.html").pipe(res)
    }

    // Get called from Client fetch call
    if (req.url === "/api/login" && req.method === "POST"){
        // User-Authentication and if user and Password are correct:
        res.writeHead(200, {'Content-Type': `text/html` });
        fs.createReadStream("./public/html/message.html").pipe(res)
    }
}).listen(3000, () => {
    console.log("Server is listening on port 3000");
});

The message.html (or any other file I tried to sent) is not displayed in the network traffic tab of the browser. So it is not sent to the client at all.
I also tried just to use res.end() or res.write(), but no file arrives at the client.

Does anybody know what I can do?