Backend PHP File Works Locally But Not On Server

I created a simple insert form page template and added it through dashboard. When the user hit submit it, it direct them to another php file – that is not created through dashboard – and redirect them back to another WordPress page.

This was working as intended on my local, but once I upload it on the server I keep getting the “File not Found” page.

form tag:

<form class="ts-form form-create-project small-12 column" id="createTimeSheetProject"
action="<?php echo get_stylesheet_directory_uri(); ?>/page-templates/time_sheet/insert_project.php"
onsubmit="return createProjectValidation()" method="post">

I’m not entirely sure where the issue reside, but I’m using an Apache server and media temple is hosting it.

my .htaccess file looks like this:

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

# END WordPress

Edit: Not sure if this is important, but the this is a subdomain site