Htaccess Remove Index.php From A URL

I looked at this: htaccess remove index.php from url but it didn't work and in the comments there seems to be disagreement on the top answer.

If I type in http://www.example.com/thanksgiving/index.php/getThankyou I get the page I want served.

If I type in http://www.example.com/thanksgiving/getThankyou I get a 404.

What I've tried in my htaccess:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^/thanksgiving/(.*)/$ /thanksgiving/index.php/$1 [L]
</IfModule>

How do I do it so /thanksgiving/getThankyou/ or any url starting with /thanksgiving in the url leads to the proper resource being served? Again, it is currently available when index.php is in the url.

I also tried: RewriteRule ^/thanksgiving/[^/]*/$ /thanksgiving/index.php/$1 [L] but that didn't work either...

Edit: It seemed part of the htaccess is being set by wordpress and may be conflicting with the desired behavior above:

The wordpress part of the same htaccess is:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

Is this interfering? How do I reconcile this with the /thanksgiving/ urls which are not part of the Wordpress application?

Edit:

The above only pertains to the root (public_html) htaccess, below is the htaccess in /thanksgiving/ itself, please analyze for conflicts, thanks for all your help!

<IfModule mod_rewrite.c>
    <IfModule mod_negotiation.c>
        Options -MultiViews
    </IfModule>

    RewriteEngine On
    RewriteBase /
    # Redirect Trailing Slashes If Not A Folder...
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule ^(.*)/$ /$1 [L,R=301]

    # Handle Front Controller...
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteRule ^ index.php [L]

    # Handle Authorization Header
    RewriteCond %{HTTP:Authorization} .
    RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
</IfModule>
# Do not change this line. 
# Change example.com to your domain name
RewriteCond %{HTTP_HOST} ^(www.)?example.com$ 

# Change your_app_name to the subfolder name
RewriteCond %{REQUEST_URI} !^/thanksgiving/ 

# Don't change the following two lines. 
RewriteCond %{REQUEST_FILENAME} !-f 
RewriteCond %{REQUEST_FILENAME} !-d 

# Change your_app_name to the subfolder name
# Change example.com to your domain name
RewriteRule ^(.*)$ /thanksgiving/$1 
RewriteCond %{HTTP_HOST} ^(www.)?example.com$
RewriteRule ^(/)?$ thanksgiving/index.php [L]