public function add_columns( $columns ) {

		$columns = array(
			'cb'             => '<input type="checkbox" />',
			'order'          => __( 'Order', 'lifterlms' ),
			'payment_status' => __( 'Payment Status', 'lifterlms' ),
			'access_status'  => __( 'Access Status', 'lifterlms' ),
			'product'        => __( 'Product', 'lifterlms' ),
			'revenue'        => __( 'Revenue', 'lifterlms' ),
			'type'           => __( 'Order Type', 'lifterlms' ),
			'order_date'     => __( 'Date', 'lifterlms' ),
		);

		return $columns;
	}