I haven't seen the domain.com's web interface at all, but generally here is how DNS works:
You have two possibilities, one is IP based (type A) dns settings. In this case you must
have a fix ip in the location where you have the NAS, so you have to type in the IP address (WAN address) of your network.
Another possibility is to create a CNAME record in the dns settings. In that case, you do not have to type in an IP address, but an another domain name -- in this case your dyndns host.
Here is a screenshot about CPanel (popular dns-setup software) to see more clearly what I'm tryint to talk about
Not sure why do you need 2 dyndns account by the way, but please look some Zone Record settings in the Domain.com web interface, and change it like this.
One more thing is that - unfortunately - you can't create CNAME record for the "main" domain, only A.
So as an example you can create a cname record to www.mydomain.com
but you cannot for the mydomain.com (so without the www. ot anything) --> only IP based (type A)
When somebody types in into the browser mydomain.com --> it should point somewhere... if you do not have a fix ip, check if you have or not 1-2MB free space which is given by the hosting company (domain.com)
If you have some space there, create a .htaccess file, which redirects the non-www url to the www.mydomain.com
Like this, when sy type in the mydomain.com, it will reach your htaccess file, which redirects to the www.mydomain.com
, which has a CNAME record point to the dyndns account, which is updated by your NAS.
Hope this helps.
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