Cannot get aws lambda function response in PHP client

Oh! well, I found the answer. You need to call the __toString() method of the GuzzleHttp\Psr7\Stream Object that is inside the Payload.

So, doing a print_r($response['Payload']->__toString()); prints "Success" which is the desired response of the Lambda function, and the one that I was looking for.

Hope this helps someone in the future.

Another way is to call, getContents() of the stream object as following:

$result = $client->invoke(array(
          // FunctionName is required
          'FunctionName' => 'myService-beta-hello',
          'InvocationType' => 'RequestResponse',
            'LogType' => 'Tail',
            'Payload' => '{"key1":"value1", "key2":"value2","key3":"value3"}',
            //'Qualifier' => 'string',
                ));
print "<pre>";
print_r($result);
print_r($result['Payload']->getContents());
print "</pre>";