paypal api curl refund getting error AUTHENTICATION_FAILURE - php

Question

I am trying to implement paypal refund using php curl.
This is my code.
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "https://api.paypal.com/v1/oauth2/token");
//curl_setopt($ch, CURLOPT_HEADER, false);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
'Accept: application/json',
'Accept-Language: en_US'
));
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_USERPWD, $clientId.":".$secret);
curl_setopt($ch, CURLOPT_POSTFIELDS, "grant_type=client_credentials");
$result = curl_exec($ch);
$json = json_decode($result);
$access_token=$json->access_token;
curl_close($ch);
$ch=curl_init();
$headers=array('Content-Type: application/json','Authorization: Bearer '.$access_token);
curl_setopt($ch,CRULOPT_HTTPHEADER,$headers);
curl_setopt($ch, CURLOPT_URL, "https://api.paypal.com/v1/payments/sale/".$paypal_transaction_id."/refund");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, "{}");
$result = curl_exec($ch);
$result_array=json_decode($result,true);
I got the access token successfully.
But, the following error occurs in refund.
"Authentication failed due to invalid authentication credentials or a
missing Authorization header."
What's wrong with my code?
Or
My PayPal account is a business account and there is no problem with receiving money (using php paypal api).
Look at https://developer.paypal.com/docs/platforms/get-started/ it says you need to fill out the PayPal Marketplaces and Platforms form to be approved.
Is this the problem?

Answer 1

Haha, I found the error.
It's just spell error.(curl_setopt($ch,CRULOPT_HTTPHEADER,$headers);)
not CRULOPT_HTTPHEADER , is CURLOPT_HTTPHEADER
and I have change code more simply.(using API v2)
$ch=curl_init();
$headers=array('Content-Type: application/json','Authorization: Basic '.base64_encode($clientId.':'.$secret));
curl_setopt($ch,CURLOPT_HTTPHEADER,$headers);
$refund_url="https://api.paypal.com/v2/payments/captures/".$order['paypal_txn_id']."/refund";
curl_setopt($ch, CURLOPT_URL, $refund_url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, "{}");
$result = curl_exec($ch);
$result_array=json_decode($result,true);
curl_close($ch);