one.com uses subdirectories as subdomains, here is a handy rewrite

.htaccess

RewriteEngine On

# redirect subdomains to matching folders
RewriteCond %{HTTPS} !=on
RewriteCond %{HTTP_HOST} !^www\. [NC]
RewriteCond %{SERVER_ADDR} !=127.0.0.1
RewriteCond %{SERVER_ADDR} !=::1
RewriteCond %{HTTP_HOST} !.*\.yourhost.com
RewriteRule ^ https://www.%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

# redirect all other traffic to main
RewriteCond %{HTTP_HOST} ^(?:www\.|)yourhost.com
RewriteCond %{REQUEST_URI} !^/main/?
RewriteRule ^(.*)$ /main/$1