[WooCommerce | Print Invoice & Packing slips] Only send invoice when order is completed

pip-invoice-email-completed.php

add_filter( 'wc_pip_invoice_email_order_status_change_trigger_actions', 'woo_custom_invoice_status', 10, 2 );
function woo_custom_invoice_status( $actions, $email_class ) {
    $actions = array(
        'woocommerce_order_status_failed_to_completed_notification',
        'woocommerce_order_status_pending_to_completed_notification',
        'woocommerce_order_status_processing_to_completed',
    );

    return $actions;
}