Echo content based on primary category

I have this code snippet

<?php
// Import necessary libraries
require_once('wp-load.php');

$post_id = get_the_ID(); // Get the current post ID
$primary_category = get_post_meta($post_id, '_yoast_wpseo_primary_category', true);
$categories = get_the_category($post_id);

if ($primary_category === 'Prezi' || $primary_category === 'Kahoot') {
echo 'A';
} elseif (count($categories) === 1 && ($categories[0]->slug === 'Prezi' || $categories[0]->slug === 'Kahoot')) {
echo 'B';
} else {
echo 'C';
}
?>

What it should do (and doesn’t at the moment)

is getting the primary category of the post. That primary category is created by the Yoas SEO plugin. When the primary category is “Prezi” or “Kahoot”, it should echo ‘A’. Wanneer there is just one category selected (and the isn’t a primary one) and that category is either “Prezi” or “Kahoot”, it should echo dan ‘B’. If the category isn’t “Prezi” or”Kahoot”, ‘C’ should be echoed.

In my case, only ‘C’ is echoed, while that categories in the posts are properly set. Is there an error in the code I don’t see?

Earlier, I had this code snippet, but is showed the parent category, always the first selected category of a post. If this code snippet could be adapted by getting the primary category and echoing ‘A’ of ‘C’, I’m happy too. Part ‘B’ isn’t that important.

<?php
$post_categories = get_the_category($post->ID);
$parent_category_name = '';

if (!empty($post_categories)) {
$parent_category = $post_categories[0]->parent ? get_category($post_categories[0]->parent) : $post_categories[0];
$parent_category_name = $parent_category->name;
}

if ($parent_category_name === 'Prezi' || $parent_category_name === 'Kahoot') {

echo
"<span>A</span>";
}
else
{
echo "<span>C</span>";
}
?>