If you also want the landing pages published on your "www" subdomain to be accessible from the root domain, you will need to create a 301 redirect in your domain registrar, redirecting domain.com to https://www.domain.com.
If the explicit redirect is not created, then the root domain will not display the page, the two URLs being separate web addresses. Google Chrome redirects this way automatically, but not all browsers do, so it's best if you create the redirect itself. That way, it will work in any browser and device.
Here's how to do this in GoDaddy:
1. Log in to your account and select the DNS settings for the domain you want to set up the redirect for.
2. Scroll down past the CNAMEs and other records to the Forwarding section.
3. Click Add next to DOMAIN.
4. Configure the settings. In this example, I used mysubdomain.mydomain.com, but you can use www.mydomain.com if you have your landing page published on your www subdomain.
That's it! Now visitors who will access mydomain.com will be redirected to mysubdomain.mydomain.com.
Note that the "www" subdomain is just like any other subdomain, and if you published on it and want your root domain to redirect to www.mydomain.com, just type www.mydomain.com instead of mysubdomain.mydomain.com in the section above.