function compareSignature($transactionData, $receivedSignature, $apiSecret) {
// Unset signature from data
unset($transactionData['signature']);
foreach ($transactionData as $key => $value) {
foreach ($value as $_key => $_value) {
$signature = hash_hmac('sha512', $dataString, $apiSecret);
if(hash_equals($receivedSignature, $signature)) {