<?php
    
$curl = curl_init();

curl_setopt_array($curl, array(
  CURLOPT_URL => "https://<your_app_subdomain>.user.com/api/public/products-by-id/:custom_id/",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "DELETE",
  CURLOPT_HTTPHEADER => array(
    "authorization: Token \<your_64_char_api_key>"
  ),
));

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}