What is the Equivalent c# method for the php "hash_hmac()"?

Question

I have a sample code in php.I need to implement this in c#.I tried the following but I am getting different values in both.

 

Please suggest me an exact hash method in c#.

 

php code: 

$signature = $this->hexToBase64(hash_hmac("sha1", $string_to_sign, self::SECRET_KEY));

private function hexToBase64($hex){
$return = "";
foreach(str_split($hex, 2) as $pair){
$return .= chr(hexdec($pair));
}
return base64_encode($return);
}

signature: ZToYIGWks4dBLImEKWozVZTkxZc= 

 

c# code: 

var key = Encoding.UTF8.GetBytes(apiKey);
string signature ;
using (var hmac = new HMACSHA1(key))
{
var hash = hmac.ComputeHash(Encoding.UTF8.GetBytes(message));
signature = Convert.ToBase64String(hash);
}

signature: wR/E2jbMo9Y87aqXllcZAynCyRE=