How can i get these values on that proccess.php
$code = '<form method="http://mydomain.com/paytm/process.php">
<input type="hidden" name="username" value="'.$gatewayusername.'" />
<input type="hidden" name="invoiceid" value="'.$invoiceid.'" />
<input type="hidden" name="amount" value="'.$amount.'" />
<input type="submit" value="Pay Now" />
</form>';
return $code;