plugin development – How to access the thank you page from the single post?

I have a thank you page on my website and I don’t want anyone can access it directly so I use the below code and it working.

add_action('template_redirect', function() {
    // ID of the thank you page
    if (!is_page(947)) { //id of page
        return;
    }

    // coming from the form, so all is fine
    if (wp_get_referer() === get_site_url().'/contact-us/') {
        return;
    }

    // we are on thank you page
    // visitor is not coming from form
    // so redirect to home
    wp_redirect(get_home_url());
    exit;
});

Now, what I am doing, I have one more form on my single post and once the user submits the form then it will redirect to the thank you page but it’s not going because I added the above code on my function.php.

So anyone knows how to access the thank you page from the single post?