Not listening to IPv4

[lusvelt]

I have multiple apps running on my server and i have installed redbird to run multiple domains on the same server, each one addressing a specific app. However when I launch redbird (via pm2) it only listens from IPv6 addresses, as I can verify by running netstat -tulpn. Is this default behaviour or is there something wrong in my configuration?

const redbird = new require('redbird')({
        port: 80,
        letsencrypt: {
                path: 'certs',
                port: 3000
        },
        ssl: {
                port: 443
        }
});