如何使用 gmail API 发送大附件

i'm trying to send an email with Gmail API. I'm able to send it with smaller files successfully. Problem appears when I try to send attachment with bigger size. It's been couple of hours I'm trying different solutions. Before it was giving error Error 413: Request Entity Too Large. I updated my code and it looks like this:

    $mime = rtrim(strtr(base64_encode($mime), '+/', '-_'), '=');
$msg = new Google_Service_Gmail_Message();
$msg->setRaw($mime);
$sendOptions = [
        'uploadType' => 'resumable'
];
// size of chunks we are going to send to google
$chunkSizeBytes = 1 * 1024 * 1024;

$client->setDefer(true);
$objSentMsg = $service->users_messages->send('me', $msg, $sendOptions);

// create mediafile upload
$media = new Google_Http_MediaFileUpload(
    $client,
    $objSentMsg,
    'message/rfc822',
    $mime,
    true,
    $chunkSizeBytes
);
//I tried to pass null in above media object in place of $mime variable. didn't worked either.


$media->setFileSize(strlen($mime));

// Upload the various chunks. $status will be false until the process is complete.
$status = false;

while (! $status) {
    $status = $media->nextChunk();
    echo $status ."<br>";
}

// Reset to the client to execute requests immediately in the future.
$client->setDefer(false);

// Get sent email message id
$googleMessageId = $result->getId();

现在它给了我错误:Uncaught Google_Service_Exception: Request is too large

顺便说一下，我尝试发送的文件是 7.x MB，在创建 mime 消息后，整个 mime 消息的大小变为 14MB 左右，发送消息的 API 限制为 35 MB.为什么它给出 Request is too large 错误.请在这方面帮助我.