In the latest version, the plug-in author has introduced checks for whether a post is password protected and it’s published. It’s this latter check that causes problems, because the post status this plug-in checks for (‘published’) doesn’t exist. A published post has the status ‘publish’. So lines 186-188 of the file class-wp-post-modal-public.php in the folder ‘public’ should NOT read:
} elseif ($post['post_status'] !== "published") {
$response = new WP_Error('post_private', 'Post is not published', array('status' => 403));
} elseif ($post['post_content'] && $post['post_status'] === "published") {
but instead
} elseif ($post['post_status'] !== "publish") {
$response = new WP_Error('post_private', 'Post is not published', array('status' => 403));
} elseif ($post['post_content'] && $post['post_status'] === "publish") {
Gee, that’s actually quite basic knowledge of WordPress.