public function init() {
        $this->slug = 'upsell';

        // Custom Fields
        add_filter( 'wpf_meta_field_groups', array( $this, 'add_meta_field_group' ), 15 );
        add_filter( 'wpf_meta_fields', array( $this, 'add_meta_fields' ) );

        // Add settings
        add_filter( 'upsell_product_field_group', array( $this, 'add_settings' ), 100, 2 );
        add_filter( 'upsell_coupon_field_group', array( $this, 'add_coupon_settings' ), 100, 2 );
        add_filter( 'wpf_configure_settings', array( $this, 'register_settings' ), 15, 2 );

        // Apply tags when order/subscription is created
        add_action( 'upsell_process_checkout_completed', array( $this, 'order_created' ) );

        // Apply tags when refunded
        add_action( 'upsell_order_status_refunded', array( $this, 'order_refunded' ) );

        // Apply tags when a subscription is cancelled
        add_action( 'upsell_subscription_soft_cancelled', array( $this, 'subscription_status_changed' ) );
        add_action( 'upsell_subscription_cancelled', array( $this, 'subscription_status_changed' ) );

        // Apply tags when a subscription payment has failed
        add_action( 'upsell_subscription_status_failed', array( $this, 'subscription_status_changed' ) );

        // Apply tags when a subscription has expired
        add_action( 'upsell_subscription_status_expired', array( $this, 'subscription_status_changed' ) );

        // Batch operations
        add_filter( 'wpf_export_options', array( $this, 'export_options' ) );
        add_filter( 'wpf_batch_upsell_init', array( $this, 'batch_init' ) );
        add_action( 'wpf_batch_upsell', array( $this, 'batch_step' ) );

    }

    /**
     * Handle subscription status changes
     *
     * @param object $sub
     */
    public function subscription_status_changed( $sub ) {

        $this->apply_tags_for_subscription_status( $sub );

        $this->sync_subscription_fields( $sub );

    }

    /**
     * Apply tags for sub status change
     *
     * @param object $sub
     */
    public function apply_tags_for_subscription_status( $sub ) {

        $status = $order->getAttribute( 'status' );

        /// do the stuff

    }

    /**
     * Sync fields for sub status change
     *
     * @param object $sub
     */
    public function sync_subscription_fields( $sub ) {

        $status = $order->getAttribute( 'status' );

        /// do the stuff

    }