我能够使用Postman将文件上传到API端点。
我试图将其转换为从表单上传文件，使用Laravel上传并使用Guzzle 6发布到端点。
它在Postman中的外观截图（我故意省略了POST URL）

下面是当你点击POSTMAN中的“生成代码”链接时生成的文本：

POST /api/file-submissions HTTP/1.1
Host: strippedhostname.com
Authorization: Basic 340r9iu34ontoeioir
Cache-Control: no-cache
Postman-Token: 6e0c3123-c07c-ce54-8ba1-0a1a402b53f1
Content-Type: multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW

----WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="FileContents"; filename=""
Content-Type: 

----WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="FileInfo"

{ "name": "_aaaa.txt", "clientNumber": "102425", "type": "Writeoff" }
----WebKitFormBoundary7MA4YWxkTrZu0gW

下面是保存文件和其他信息的控制器功能。文件上传正确，我能够得到文件信息。
我认为我遇到的问题是用正确的数据设置multipart和header数组。

public function fileUploadPost(Request $request)
{
    $data_posted = $request->input();
    $endpoint = "/file-submissions";
    $response = array();
    $file = $request->file('filename');
    $name = time() . '_' . $file->getClientOriginalName();
    $path = base_path() .'/public_html/documents/';

    $resource = fopen($file,"r") or die("File upload Problems");

    $file->move($path, $name);

    // { "name": "test_upload.txt", "clientNumber": "102425", "type": "Writeoff" }
    $fileinfo = array(
        'name'          =>  $name,
        'clientNumber'  =>  "102425",
        'type'          =>  'Writeoff',
    );

    $client = new \GuzzleHttp\Client();

    $res = $client->request('POST', $this->base_api . $endpoint, [
        'auth' => [env('API_USERNAME'), env('API_PASSWORD')],
        'multipart' => [
            [
                'name'  =>  $name,
                'FileContents'  => fopen($path . $name, 'r'),
                'contents'      => fopen($path . $name, 'r'),
                'FileInfo'      => json_encode($fileinfo),
                'headers'       =>  [
                    'Content-Type' => 'text/plain',
                    'Content-Disposition'   => 'form-data; name="FileContents"; filename="'. $name .'"',
                ],
                // 'contents' => $resource,
            ]
        ],
    ]);

    if($res->getStatusCode() != 200) exit("Something happened, could not retrieve data");

    $response = json_decode($res->getBody());

    var_dump($response);
    exit();
}

我收到的错误，使用Laravel的调试视图显示的屏幕截图：