Easy! You have a couple of options to do so.
The easiest one, but less safe, is to create a brand new PHP file in the root folder of WordPress. Let’s say we will call it get_post.php and add WordPress functionality to it.
Like so:
<?php
require_once('wp-load.php'); // add wordpress functionality
$post = $_POST;
if ( $something ) // security check
update_post_meta( $post['post_id'], 'post_data', $post );
?>
The API link will be yourdomain.com/get_posts.php
Another option is to create a brand new page template inside of your template directory. And create a page using that template within your WordPress dashboard.
<?php
/* Template Name: Api Template */
if ( ! defined( ‘ABSPATH’ ) ) {
exit;
}
$post = $_POST;
update_post_meta( $post['post_id'], 'post_data', $post );
?>
The API link will be: yourdomain.com/newly-created-page-permalink.