Nikhil I suppose it's just an HTTPS issue. You need a redirect service that will have a certificate for your domain.
WWW-izer claim they do, but I suppose it's only for their paid plan.
Maybe GoDaddy does setup a certificate for you, I don't know.
If you host your DNS with Namecheap or Cloudflare you could use an "ANAME" record and let FreeFlarum take care of it (as described in their docs), but it requires an hosting that supports one of those fakes CNAMEs. Or if you use Cloudflare you could even setup the redirect right in Cloudflare and it would be HTTPS-enabled.
If you stay on GoDaddy DNS and can't setup the HTTPS redirect, maybe contact the FreeFlarum support email and ask if you can setup an A record to FreeFlarum instead. Maybe they can allow it for you, but there's good reasons they wouldn't offer it in the official docs.