Add Plugins

I have set up my multisite installation in a directory inside of “public_html” (instead of the “public_html” folder) on a shared host via bluehost.com. I’m using subdomains for my subsites instead of subdirectories. My “.htaccess” file includes the code below:

# Use PHP5.6 Single php.ini as default
        AddHandler application/x-httpd-phpbetas .php
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^(wp-(content|admin|includes).*) titanstartup/$1 [L]
RewriteRule ^(.*\.php)$ titanstartup/$1 [L]
RewriteRule . index.php [L]

Everything seems to work fine, except I cannot Add New Plugins or themes. When I activate Dev Tools in Chrome, the console logs a 403 (Forbidden) error when trying to access wp-admin/admin-ajax.php. My directory permissions for wp-admin are 755 and my file permissions for admin-ajax.php are 644.

I am trying to do this as the Super Admin. I’m stumped as to why this isn’t working properly.

I CAN add and update plugins and themes via FTP, but I’d really like to be able to do this from the dashboard so I can more safely give members of my team this ability without giving them FTP access.

I’m running the Divi theme from elegantthemes.com on most of the subsites if that makes a difference. Any help would be very much appreciated.