Installing PHP application in sub-directory and coexist with WordPress

I have a website with WordPress installed and fully functional.

I also installed a custom PHP application we developed for our needs in a sub-directory off of the root folder.

When I try to access the /app/index.php or /app/index.html I get my WordPress website return a file not found. How can I allow access to that app?

My current WordPress .htaccess file looks like:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

And my Apps sub-directory .htaccess file looks like:

DirectoryIndex index.php

<FilesMatch “\.(php|inc)$”>
Order allow,deny
deny from all
</FilesMatch>
<FilesMatch “(index.php|dl.php|ut.php|lt.php|download.php)$”>
Order allow,deny
allow from all
</FilesMatch>
php_flag magic_quotes_gpc on

Thank you in advance for your help with this!!!