Dropbox API cURL request error: "options: expected array, got string" - php

Question

I try to make a cURL request to Dropbox API, but I get this error:
Error in call to API function "files/search_v2": options: expected array, got string
I don't understand why, I'm sending an array!?
My code is below. Documentation here: https://www.dropbox.com/developers/documentation/http/documentation#files-search
$token = "....";
$options = array("path" => "/", "max_results" => 10);
$options["file_categories"] = "folder";
$parameters = array("query" => "searchPhrase", "options" => $options);
$headers = array(
"Authorization: Bearer $token",
'Content-Type: application/json'
);
$curlOptions = array(
CURLOPT_HTTPHEADER => $headers,
CURLOPT_POST => true,
CURLOPT_POSTFIELDS => json_encode($parameters),
CURLOPT_RETURNTRANSFER => true,
CURLOPT_VERBOSE => true,
CURLOPT_SSL_VERIFYHOST => false,
CURLOPT_SSL_VERIFYPEER => false
);
try {
$ch = curl_init('https://api.dropboxapi.com/2/files/search_v2');
curl_setopt_array($ch, $curlOptions);
$response = curl_exec($ch);
//var_dump($response);
curl_close($ch);
} catch (Exception $e) {
trigger_error(
sprintf(
'Curl failed with error #%d: %s',
$e->getCode(),
$e->getMessage()
),
E_USER_ERROR
);
}