// URL
$url = 'https://api.eu.sparkpost.com/api/v1/recipient-validation/single/ab@northfinance.dk';

// CURL
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_USERPWD, 'API_KEY');
curl_setopt($ch, CURLOPT_HTTPHEADER, ['Content-Type: application/json']);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_TIMEOUT, 10);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);

// RESULT
$result = json_decode(curl_exec($ch), true);
$http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
curl_close($ch);

echo $result;
die();