How to convert nonce to string?

Question

How do i convert certificates, nonce and nonceString data to a String? When i try to convert the nonce, nonceSigntaute to string with UTF8 encoding it's failing.

func addPaymentPassViewController(_ controller: PKAddPaymentPassViewController, 
    generateRequestWithCertificateChain certificates: [Data], 
    nonce: Data, 
    nonceSignature: Data, 
    completionHandler handler: @escaping (PKAddPaymentPassRequest) -> Void) {

  ...
}