In order to include and execute PHP code in your .HTML/.HTM pages, you should set the PHP as the default handler for these pages. You can easily achieve this by adding the following line to your .htaccess:
AddHandler application/x-httpd-lsphp .php .html .htm .phtml
The PHP code should be valid and placed between PHP opening <?php and closing ?> tags.
If you notice any problems or if you require any further assistance please open a new support ticket from your Dashboard and we’ll be happy to help you.