PHP向API发送curl请求

我有一个使用Java脚本的API调用，它的工作方式非常棒:

var headers = {
  Authorization: "Bearer " + MY_ACCESS_TOKEN
};

var requestParams = {
  method: "POST",
  contentType: "application/json",
  headers: headers,
  payload: JSON.stringify({
    query: 'query {adSet(id: "' + MY_ADSET_ID + '") {insights(timeRange: {from: "2023-08-01T00:00:00Z", until: "2023-08-10T23:59:59Z"}timeIncrement: DAILY) {timestamps reports {impressions conversions offerwallImpressions offerwallAverageRank spend}}}}'
  })

var response = UrlFetchApp.fetch(MY_API_ENDPOINT, requestParams);
var data = JSON.parse(response);

When I try to convert this to PHP I simply get a blank repsonse from the API. What am I doing wrong?
Note that my_curl () works correctly when I use it to retrieve $MY_ACCESS_TOKEN from the API.

$postdata = json_encode('query: query {adSet(id: "' . $MY_ADSET_ID . '") {insights(timeRange: {from: "2023-08-01T00:00:00Z", until: "2023-08-10T23:59:59Z"} timeIncrement: DAILY) {timestamps reports {impressions conversions offerwallImpressions offerwallAverageRank spend}}}}');
$endpoint = $MY_API_ENDPOINT;
$headers = array (
    "Content-Type: application/json",
    "Authorization: Bearer " . $MY_ACCESS_TOKEN,
    $postdata
);

$data = my_curl ($endpoint, $headers);
var_dump ($data);

function my_curl ($endpoint, $headers) {
    $ch = curl_init ();

    curl_setopt ($ch, CURLOPT_URL, $endpoint);
    curl_setopt ($ch, CURLOPT_POST, 1);
    curl_setopt ($ch, CURLOPT_HTTPHEADER, $headers);
    curl_setopt ($ch, CURLOPT_HEADER, false);
    curl_setopt ($ch, CURLOPT_RETURNTRANSFER, true);

    $server_output = curl_exec($ch);
    curl_close ($ch);

    $json = json_decode ($server_output, true);

    return ($json);
}