WHCMS stuff

<?php
add_hook('CartTotalAdjustment', 1, function($vars) {
    $cart_adjustments = array();

    // Number of NAT services to buy before applying discount
    $PRODUCT_THRESHOLD = 3;

    // Product ids discount is applied to
    $NAT_PRODUCT_IDS = array(232, 42, 321, 321, 321, 21);

    // Holds product ID's that are in customer basket
    $selectedProductIds = [];

    // Store product ID's in a separate array
    foreach ($vars['products'] as $product) {
        $selectedProductIds[] = $product['pid'];
    }

    // Check if the number of intersected id's exceeds threshold
    if (count(array_intersect($selectedProductIds, $NAT_PRODUCT_IDS)) >= $PRODUCT_THRESHOLD) {
        $cart_adjustments = [
            "description" => "Custom discount for buying " . $PRODUCT_THRESHOLD . " number of NAT services",
            "amount" => "-10.00",
            "taxed" => false,
        ];
    }
    return $cart_adjustments;
});