Why is my site which resides in a subfolder broken when visiting it through a subdomain URL?
From your description it looks like you need to

add your subdomain to proper site folder. Check your sites.php to be correct, for example-



Check your settings.php to allow your sub-domain as per the documentation-



Check if image urls are hard coded

Cache or CDN plugin are affecting it.


Adding the type of error you are getting could let us help you better.