Can someone take me through the process of getting clean blog post URLs

I've got things working on the default setting but I'm doing the following and getting errors:

1. htaccess file

Note my /blog/ folder containing the blog post template is at /posts/ otherwise my blog page won't load due to filename extension stripping out.

RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteCond %{REQUEST_FILENAME}.php -f RewriteRule ^(.+)$ $1.php [L,QSA]

redirect html pages to the root domain

RewriteRule ^index.html$ / [NC,R,L]

<IfModule mod_rewrite.c>
RewriteEngine on
RewriteRule ^blog/([a-zA-Z0-9-/]+)$ /posts/post.php?s=$1 [L] </IfModule>

1. Changing the Blog post page path in the CMS settings to:

/posts/{postSlug}

1. I'm calling the blog post in the /posts/post.php file thus:

   <div class="post"> <?php perch_blog_post(perch_get('s')); ?>

           <div class="meta">
               <div class="cats">
                   <?php perch_blog_post_categories(perch_get('s')); ?>
               </div>
               <div class="tags">
                   <?php perch_blog_post_tags(perch_get('s')); ?>
               </div>
           </div>
   
   
   
       </div>
   

2. I'm calling the blog post with this code:

<?php perch_blog_section('blog'); ?> <?php perch_blog_custom(array( 'section' => 'blog', 'template' => 'post_in_list.html', ));?>

The URLs I'm getting are:

https://www.website.com/posts/a-test-blog-post

So I believe it's looking in the correct folder for the blog template being /posts/ but I get a 404 error.