Token request getting HTTP ERROR 500 , using API by PHP cURL

trying to using an API which calling by an external link and basic token authorization.
it has 3 steps like :
1- asking for token ( every half an hour)
2- pass the token to another combo box to getting result by bearer token
3- passing same bearer token to another combo box for fetching data .
everything works fine (getting token from POSTMAN) but the problem is starting when requesting php curl calling straightforward in the codes which gives me : HTTP ERROR 500 (have to refresh token request every half an hour)
here is the code:

<?php

$curl = curl_init();

curl_setopt_array($curl, array(
 CURLOPT_URL => 'https://api.rasatpa.ir/auth/oauth/token',
 CURLOPT_RETURNTRANSFER => true,
 CURLOPT_ENCODING => '',
 CURLOPT_MAXREDIRS => 10,
 CURLOPT_TIMEOUT => 0,
 CURLOPT_FOLLOWLOCATION => true,
 CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
 CURLOPT_CUSTOMREQUEST => 'POST',
 CURLOPT_POSTFIELDS => array(,,),
 CURLOPT_HTTPHEADER => array(
   'Authorization: Basic YXRpeWVoSGNwV3M6QHRpeWUkd3NAdXNlcg=='
 ),
));

$response = curl_exec($curl);

curl_close($curl);
echo $response;

?>