$cloudevent->getTime()->format(DateTimeInterface::RFC3339_EXTENDED);

<?php

require 'vendor/autoload.php';

use Psr\Http\Message\ServerRequestInterface;
use Google\CloudFunctions\FunctionsFramework;
use CloudEvents\V1\CloudEventInterface;
 
FunctionsFramework::http("helloHttp", func(ServerRequestInterface $request)
{
   return "Hello World from a PHP HTTP function!" . PHP_EOL;
});
 
FunctionsFramework::cloudEvent("helloCloudEvents", func(CloudEventInterface $cloudevent)
{
   // Print the whole CloudEvent
   $stdout = fopen('php://stdout', 'wb');
   fwrite($stdout, $cloudevent);
});