Vanilla API v2 Post Request (Curl) not working? - api

Question

I'm trying to add a new user to my Vanilla forum and unfortunately I don't understand what's wrong with my code. GET request to read user data works fine butPOST requests result in a "bool(false)".
As I understand it, that's already a response from the API, which obviously can't do anything with my request, right?
But what's wrong with that? Do I have to somehow send the JSON data as a 'body'? Anyone have an idea? Thank you!!!
This is what my code currently looks like:
<?php
// post with absolute url = Invalid CSRF token error
// $url = "https://example.com/app/vanilla/api/v2/users";
$url = "/app/vanilla/api/v2/users";
$curl = curl_init($url);
curl_setopt($curl, CURLOPT_URL, $url);
$headers = array(
"Accept: application/json",
"Authorization: Bearer {va.jOh189hry7463klur_kcw8UomJU36782.HGqvdQ.RQon456}"
);
$data = array(
'bypassSpam' => 'false',
'email' => 'info#mysite.de',
'emailConfirmed' => 'true',
'name' => 'Theo Tester',
'password' => '1234567890',
'photo' => '',
'roleID' => [33]
);
$payload = json_encode(array($data));
// Attach encoded JSON string to the POST fields
curl_setopt($curl, CURLOPT_POSTFIELDS, $payload);
// Set the content type to application/json
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);
// Return response instead of outputting
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
//for debug only!
curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
$resp = curl_exec($curl);
curl_close($curl);
var_dump($resp);
?>
This is what the vanilla API documentation looks like (please see picture below or link):
(https://success.vanillaforums.com/kb/articles/202-api-v2-reference-endpoints#/Users/post_users)
And this just for completeness is the code for GET requests as it works for me:
<?php
$url = "https://example.com/app/vanilla/api/v2/roles";
$curl = curl_init($url);
curl_setopt($curl, CURLOPT_URL, $url);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
$headers = array(
"Accept: application/json",
"Authorization: Bearer {va.jOh189hry7463klur_kcw8UomJU36782.HGqvdQ.RQon456}",
);
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);
//for debug only!
curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
$resp = curl_exec($curl);
curl_close($curl);
var_dump($resp);
?>