Currently this feature will only work with Cloudflare and is therefore required for creating custom domains.
To manage your domain with Cloudflare, and to create an SSL certificate, please visit Cloudflare.
By default, Nubo creates a URL for your service, e.g. express.nubo.dev.
If you would like to create a custom domain for your service, simply select Manage Domains.
Enter your custom domain name.
Now head over to your domain registrar and create a CNAME record for your domain and point it to global.nubo.app.
You can also create a record for a subdomain. Follow the same steps at your registrar to create a CNAME record.