Getting "not authorised to perform the operation." while trying to combinepdf

Here's the code:

$url="https://pdf-services-ue1.adobe.io/token";
$headers=array(
  'Content-Type:application/x-www-form-urlencoded',
);
$ch=curl_init();
curl_setopt($ch,CURLOPT_URL,$url);
curl_setopt($ch,CURLOPT_POST,true);
curl_setopt($ch,CURLOPT_POSTFIELDS,"client_id={$cmyclientid}&client_secret={$mysecret}");
curl_setopt($ch,CURLOPT_HTTPHEADER,$headers);
curl_setopt($ch,CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch,CURLINFO_HEADER_OUT,true);
$response=curl_exec($ch);
curl_close($ch);
$token=json_decode($response,true);
//URL FILE 1 -----------------------------------------------------------------------------
$url="https://pdf-services-ue1.adobe.io/assets";
$headers=array(
  'Content-Type:application/json',
	"Authorization:Bearer {$token['access_token']}",
	"x-api-key: {$cmyclientid}",
);
$ch=curl_init();
curl_setopt($ch,CURLOPT_URL,$url);
curl_setopt($ch,CURLOPT_POST,true);
curl_setopt($ch,CURLOPT_POSTFIELDS,'{"mediaType":"application/pdf"}');
curl_setopt($ch,CURLOPT_HTTPHEADER,$headers);
curl_setopt($ch,CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch,CURLINFO_HEADER_OUT,true);
$response=curl_exec($ch);
curl_close($ch);
$asset1=json_decode($response,true);
//UPLOAD FILE 1 -----------------------------------------------------------------------------
$url=$asset1['uploadUri'];
$headers=array(
  'Content-Type: application/pdf',
);
$ch=curl_init();
curl_setopt($ch,CURLOPT_URL,$url);
curl_setopt($ch,CURLOPT_CUSTOMREQUEST,'PUT');
curl_setopt($ch,CURLOPT_POSTFIELDS,file_get_contents('Manual-ENG-HopperCD-Discriminator-II.pdf'));
curl_setopt($ch,CURLOPT_HTTPHEADER,$headers);
curl_setopt($ch,CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch,CURLINFO_HEADER_OUT,true);
$response=curl_exec($ch);
curl_close($ch);
//URL FILE 2 -----------------------------------------------------------------------------
$url="https://pdf-services-ue1.adobe.io/assets";
$headers=array(
  'Content-Type:application/json',
	"Authorization:Bearer {$token['access_token']}",
	"x-api-key: {$cmyclientid}",
);
$ch=curl_init();
curl_setopt($ch,CURLOPT_URL,$url);
curl_setopt($ch,CURLOPT_POST,true);
curl_setopt($ch,CURLOPT_POSTFIELDS,'{"mediaType":"application/pdf"}');
curl_setopt($ch,CURLOPT_HTTPHEADER,$headers);
curl_setopt($ch,CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch,CURLINFO_HEADER_OUT,true);
$response=curl_exec($ch);
curl_close($ch);
$asset2=json_decode($response,true);
//UPLOAD FILE 2 -----------------------------------------------------------------------------
$url=$asset2['uploadUri'];
$headers=array(
  'Content-Type: application/pdf',
);
$ch=curl_init();
curl_setopt($ch,CURLOPT_URL,$url);
curl_setopt($ch,CURLOPT_CUSTOMREQUEST,'PUT');
curl_setopt($ch,CURLOPT_POSTFIELDS,file_get_contents('modulo_imposta_bollo.pdf'));
curl_setopt($ch,CURLOPT_HTTPHEADER,$headers);
curl_setopt($ch,CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch,CURLINFO_HEADER_OUT,true);
$response=curl_exec($ch);
curl_close($ch);
//COMBINE FILE -----------------------------------------------------------------------------
$url="https://pdf-services-ue1.adobe.io/operation/combinepdf";
$headers=array(
  'Content-Type:application/json',
	"Authorization:Bearer {$token['access_token']}",
	"x-api-key: {$cmyclientid}",
);
$body='{"assets":[{"assetID":"'.$asset1['assetID'].'"},{"assetID":"'.$asset2['assetID'].'"}]}';
$ch=curl_init();
curl_setopt($ch,CURLOPT_URL,$url);
curl_setopt($ch,CURLOPT_POST,true);
curl_setopt($ch,CURLOPT_POSTFIELDS,$body);
curl_setopt($ch,CURLOPT_HTTPHEADER,$headers);
curl_setopt($ch,CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch,CURLINFO_HEADER_OUT,true);
echo $response=curl_exec($ch);
curl_close($ch);
$information=curl_getinfo($ch);
print_r($information);