This is my .htaccess located at public_html
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteRule ^$ app/webroot/ [L]
RewriteRule (.*) app/webroot/$1 [L]
</IfModule>
I have a (legacy) CakePHP app running in public_html/app for maindomain.com
I added an addon domain otherdomain.com under public_html/otherdomain. However, when trying to load the index page it returns a 500 server error.
Removing the public_html/.htaccess permits browsing otherdomain.com correctly, but the CakePHP app (maindomain.com) then has routing issues.
This is the CakePHP .htaccess under public_html/app:
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteRule ^$ webroot/ [L]
RewriteRule (.*) webroot/$1 [L]
</IfModule>
it appears that your main htaccess is redirecting traffic to your app/webroot/ which is causing problems for otherdomain.com. Maybe you can check the hostname that is entered and redirect based on that. Something like this.
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{HTTP_HOST} ^maindomain\.com [NC]
RewriteRule ^(.*)$ app/webroot/$1 [L]
RewriteCond %{HTTP_HOST} ^otherdomain\.com [NC]
RewriteRule (.*) http://otherdomain.com/$1 [L]
</IfModule>