Required. The public encryption key the Value Added Services protocol uses.
Use a Base64-encoded X.509 SubjectPublicKeyInfo structure that contains an ECDH public key for group P256.
Required. The payload the device transmits to the Apple Pay terminal.
The size must be no more than 64 bytes. The system truncates messages longer than 64 bytes.
Required. Text encoding that is used to convert the message from the string representation
to a data representation to render the barcode. The value is typically iso-8859-1, but you may
use another encoding that is supported by your barcode scanning infrastructure.