Pointing my Smugmug Site to a Subdomain of my Wordpress Site

Hi all,

Novice at web stuff here.

I've moved my main domain name (www.jamesvernacotola.com) to a wordpress.org hosted site, and would like to turn my Smugmug page (jimmyv99.smugmug.com) into a subdomain named 'photos.jamesvernacotola.com'.

After plenty of trial and error and searching on this forum, and Youtube watching, I haven't been able to make it happen yet.

My domain name is registered at GoDaddy and my hosting is on Siteground if that's relevant.

Some of the directions that I've seen say that I need to change something in my CNAME but it looks like I don't have access to that in my GoDaddy account, based on the message on my DNS Management page under "Records" that says "We can't display your DNS information because your nameservers aren't managed by us."

So here's what I've done so far:

In the DNS zone editor in my Siteground account:
I added a CNAME with the following values:
Name: photos.jamesvernacotola.com
TTL: 14400
CNAME: domains.smugmug.com

In my GoDaddy account:
I attempted to add a subdomain to the "Forwarding" section.
I put "photos" for Subdomain and Forward to https://jimmyv99.smugmug.com.
I chose Permanent (301) and Forward only, though I imagine I would ultimately want Fowrard with masking?

Finally, in my Smugmug account:
Under Account Information, I entered as my Custom Domain: photos.jamesvernacotola.com

I know this has been discussed before and I've found a couple links on this forum that look like they go to instructions for this, but they both lead to pages that don't exist anymore on the Smugmug help page.

Is there something I'm missing?

Thanks very much for any help you can provide.