Test case script

<?php

$handle = curl_init('https://content.dropboxapi.com/2/files/download');

$out_handle = fopen('output.tmp', 'w');

$options = array(
    41 => 1,
    42 => 1,
    2 => false,
    19913 => 1,
    52 => false,
    64 => 1,
    CURLOPT_HTTPHEADER => array(
        'Authorization: Bearer (snipped valid bearer)',
        'Content-Type:',
        'Dropbox-API-Arg: {"path":"/(snipped valid path)"}',
    ),
    47 => 1,
    10001 => $out_handle,
    19914 => 1,
    45 => false,
    10104 => array(400),
);

curl_setopt_array($handle, $options);

$response = curl_exec($handle);
$error = curl_error($handle);
$getinfo = curl_getinfo($handle);

curl_close($handle);

var_dump($error);
var_dump($response);