Example: Woo reward based on percentage

/**
 * Woo Point Rewards by Category
 * Reward buyes with points for buying products.
 * @version 1.0
 */
function mycred_woo_payout_reward_per_category( $order_id ) {

    // Make sure we do not crash our site if myCRED gets disabled
    if ( ! function_exists( 'mycred' ) ) return;

    // Setup
    $payouts = array(
        'category-one'   => 10,
        'category-two'   => 15,
        'category-three' => 20
    );

    // Get Order
    $order = wc_get_order( $order_id );

    // Get items in order
    $items = $order->get_items();

    $reward = 0;

    // Loop through each item to get the category they are in
    foreach ( $items as $item ) {

        $product_id = absint( $item['product_id'] );

        // Get all the categories this product is in
        $categories = wp_get_object_terms( $product_id, 'product_cat', array( 'fields' => 'slugs' ) );

        // Default payout is 10%
        $percentage_to_pay = 10;

        if ( ! empty( $categories ) ) {

            // Assuming each product is only in maximum 1 category!
            $category_slug = $categories[0];

            // Find where our category slug fits in our $payouts setup
            if ( array_key_exists( $category_slug, $payouts ) )
                $percentage_to_pay = $payouts[ $category_slug ];

        }

        // Calculate reward = x (percentage) of ( product price x quantity )
        $reward += ( ( $item['line_subtotal'] * $item['qty'] ) * ( 1 + ( $percentage_to_pay / 100 ) ) );

    }

    // Zero points = no payout
    if ( $reward == 0 ) return;

    // Load myCRED
    $mycred = mycred();

    // Make sure we only payout once per order
    if ( ! $mycred->has_entry( 'reward', $order_id, $order->user_id ) )
        $mycred->add_creds(
            'reward',
            $order->user_id,
            $reward,
            'Points reward for store purchase',
            $order_id,
            array( 'ref_type' => 'post' )
        );

}
add_action( 'woocommerce_payment_complete', 'mycred_woo_payout_reward_per_category' );