*To generate the checksum use below string and secrect_ with HMAC SHA256.*
The secrectkey to be used, which is your account password.
$string= Token:Your Register Mobile
Expample : ZKEY01fbb15e8098dd8970e5c665:9432839941
$secret = Your ZuelPay Account Password
$signature = hash_hmac('sha256', $string, $secret)