Your screenshot shows the ZD1200 still has the default Ruckus certificate so if you bought a server certificate for your ZD then it hasn't successfully uploaded. Your connection is flagged as insecure because the default self-signed ZD certificate wasn't issued by a trusted CA and its CN doesn't match the hostname in your URL (which is just an IP address).
One thing to watch for is that the ZD1200 only supports RSA certificates so don't get yourself an ECDSA certificate.
You'll know if you've successfully uploaded your new certificate because the ZD will automatically redirect all http requests to https://<your-cert's-FQDN>. (So you need to ensure your devices can resolve this - either via a DNS A/CNAME record or by adding the ZD to the host overrides list in your firewall's DNS settings).
