Not Able to Create a Certificate in Synology DSM

Hmm. You have two IP addresses for that domain name in your DNS. Do you have GoDaddy Domain Forwarding enabled? If so, you should disable that and ensure the IP A record is for the public IP of your system.

From the Let's Debug "verbose" output

A and AAAA records found for this domain
rocknas.net. 0 IN A 76.223.105.230
rocknas.net. 0 IN A 13.248.243.5

I know you said you used a CNAME but I don't see that. See below for GoDaddy DNS instructions