Cancel Shipstation API Issue PHP - php

Question

I'm trying to cancel the order from Shipstation for That I've write a code
$curl = curl_init();
curl_setopt_array($curl, array(
CURLOPT_URL => "https://ssapi.shipstation.com/orders/".$order_id,
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 0,
CURLOPT_FOLLOWLOCATION => true,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "DELETE",
CURLOPT_USERPWD => "$public_key:$private_key",
));
$response = curl_exec($curl);
curl_close($curl);
echo $response;
echo "here";
now when I run this API it returns nothing no error no issue no success message same order is also not deleted from Shipstation when I try to pass wrong Public or Private key then it gives me an Error
401 Unauthorized
it means that API call is going correctly because I'm getting response but when I pass the correct creds then it gives no response.
Edit
Now I'm trying
$curl = curl_init();
curl_setopt_array($curl, array(
CURLOPT_URL => "https://ssapi.shipstation.com/orders/".$order_id,
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 0,
CURLOPT_FOLLOWLOCATION => true,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "DELETE",
CURLOPT_HTTPHEADER => array(
"Host: ssapi.shipstation.com",
"Authorization:Basic __MY_AUTH_HERE__",
),
));
$response = curl_exec($curl);
curl_close($curl);
echo $response;
Now it is giving me an Error
{"Message":"Authorization has been denied for this request."}
where I've created my Auth like
$auth = base64_encode($username_api_key.":". $password_api_secret);
What is the issue and how to fix that?
Thanks