function XXXXX($string)
{
$key = 'XXXXX'; // Had to be 24 in length for 3DES cipher
$iv = 'XXXXX'; // Had to be 8 in length

// Encrypt String
$encrypted_string = mcrypt_encrypt(MCRYPT_3DES, $key, $string, MCRYPT_MODE_CBC, $iv);
$encoded_string = base64_encode($encrypted_string);

return $iv . $encoded_string;
}

<?php echo epay_url_encrypt_custnum($this->getCustomer()->getTaxvat()) ?>

<a href="https://securewebsite.com/urlstuff<?php echo epay_url_encrypt_custnum($this->getCustomer()->getTaxvat()) ?>>TEXT FOR LINK</a>