我在用的实例，供参考：

<?php
require_once('./vendor/autoload.php');

use WeChatPay\Builder;
use WeChatPay\Crypto\Rsa;
use WeChatPay\Crypto\Hash;
use GuzzleHttp\Psr7\Uri;
use GuzzleHttp\Psr7\Utils;
use GuzzleHttp\Psr7\InflateStream;
use Psr\Http\Message\ResponseInterface;

$instance = Builder::factory([
    'mchid'      => '',
    'serial'     => '',
    'privateKey' => $privateKey,
    'certs'      => ['' => $publicKey],
]);
$handler = clone $instance->getDriver()->select()->getConfig('handler');
$handler->remove('verifier');

$tradeBill = $instance
    ->v3->bill->tradebill
    ->getAsync([
        'query' => [
            'bill_date' => $billDate,
            'bill_type' => 'ALL',
            'tar_type'  => 'GZIP',
        ],
    ])
    ->then(static function(ResponseInterface $response) {
        return (array) json_decode($response->getBody()->getContents(), true);
    })
    ->wait();

$hashAlgo  = strtolower($tradeBill['hash_type'] ?? 'sha1');
$hashValue = $tradeBill['hash_value'] ?? null;
$previous  = new Uri($tradeBill['download_url'] ?? '');
$baseUri   = $previous->composeComponents($previous->getScheme(), $previous->getAuthority(), '/', '', '');

$savedTo = fopen('/tmp/all.' . $billDate . '.csv.gz', 'w+');
$stream  = Utils::streamFor($savedTo);

$message = $instance
    ->chain(ltrim($previous->getPath(), '/'))
    ->getAsync([
        'sink'     => $stream,
        'handler'  => $handler,
        'query'    => $previous->getQuery(),
        'base_uri' => $baseUri,
    ])
    ->then(static function(ResponseInterface $response) use($hashValue, $hashAlgo) {
        if (Hash::equals(Utils::hash(new InflateStream($response->getBody()), $hashAlgo), $hashValue)) {
            return 'Verified with digest(' . $hashValue . ') OK';
        }
        $response->getBody()->close();
        throw new UnexpectedValueException('Bad digest verification');
    })
    ->wait();

print_r($message);