Pushover for WooCommerce - Add order coupon codes to message

functions.php

add_filter(
	'wc_pushover_notify_new_order',
	function ( $args ) {
		$order = wc_get_order( $args['order_id'] );

		if ( ! $order ) {
			return $args;
		}

		$order_coupons = $order->get_items( 'coupon' );

		if ( ! $order_coupons ) {
			return $args;
		}

		$args['message'] .= sprintf(
			' (%s)',
			implode(
				',',
				array_map(
					function ( $el ) {
						return $el->get_code();
					},
					$order_coupons
				)
			)
		);

		return $args;
	}
);