Recently my organization connected our domain to WIX. Previously we were with Westhost. However, our email and forum were sub-directories from our Westhost account. (marinaoutrigger.org/forum) Now we get a 404 error obviously because the content doesn't exist on the WIX IP. I created a sub-domain (forum.marianoutrigger.org) and put the original IP of our DNS host and now the index page displays, but nothing from the sub folders.
Is there any way to keep the original marinaoutrigger.org/forum or how do I get the files withing the "forum" directory to propagate through the sub-domain?
After visiting your site and using the inspector, I can see that all of your CSS and images on the forum subdomain are 404ing. If I change the URL to your new subdomain, and remove the /forum, I am getting the images and CSS to load.
Additionally, I can see that links on your forum (which display correctly on the home page) still point to your old domain (that is now hosted on Wix.) This means you have a couple seperate issues that need to be resolved.
To keep your current setup
At minimum, you will need to update settings for your simple machines forum to supply a new base URL. That will be required to have the forum provide links that start with your forum.marianoutrigger.org subdomain.
Ideally, this will also update your theme to point images, CSS, and links to the correct location. If not, you can utilize the mod rewrite file to strip the forum directory from requests. A rule like this is a good base to do that:
RewriteRule ^forum/(.*)$ /$1 [L,NC,R]
To reverse proxy to Wix
Another solution you could do is have your (old) Westhost site still host your domain as it did before. Leave your forum inside /forum, and reverse-proxy other content over to the Wix site. This basically means that Westhost would keep your domain, host your /forum, and any other requests it gets it would forward to Wix, recieve the response, and transparently send that to the user.
This strategy has several advantages, such as leaving all URLs the same (an SEO benefit, and limiting your cleanup.)
Apache has a basic example in their documentation. I've adapted it to give you a little nudge in the right direction (assuming your wix site is reachable via example.wix.com):
RewriteCond %{REQUEST_URI} !^/(forum)(.*)$
RewriteCond "%{REQUEST_FILENAME}" !-f
RewriteCond "%{REQUEST_FILENAME}" !-d
RewriteRule "^/(.*)" "http://example.wix.com/$1" [P]
ProxyPassReverse "/" "http://example.wix.com/"
Note: