使用php guzzle for PUT与流和参数

Question

I'm trying to figure out how to implement the following REST PUT using Guzzle. I've tried using multipart and json, but I'm not sure what the syntax should be for having the parameters with a streamed xml file.

Can anyone help me translate this into a proper query? Below is what I tried so far, but it returns an error because it says the ProjectXML must be included.

$newUri = sprintf('%s/projects/%s/storage', $api_base, $testPid);
$newResp = $client->put($newUri,
    [
        'headers'         => [
            'Authorization' => sprintf("HubApi %s", $api_key),
        ],
        'multipart' => [
            [
                'name'     => 'ProjectXml',
                'contents' => file_get_contents("xml/$testPid.xml")
            ],
            [
                'name' => 'ProjectId',
                'contents' => $testPid
            ],
            [
                'name' => 'HubUserId',
                'contents' => "xxxxxxx-xxxxx-xxxx-xxxxx-xxxxxxxx"
            ],
            [
                'name' => 'ProductId',
                'contents' => "$(package:ourcompany/ourproducttype)/products/ProductABC123"
            ],
            [
                'name' => 'ThemeUrl',
                'contents' => "$(package:ourcompany/ourproducttype)/themes/themename-white-Classic"
            ],

        ]
    ]
);

Response:

`400 Bad Request - Validation Error` response:
{"code":"RequestValidationError","message":"'Project Xml' should not be empty."}