Serialise an invoice to the base64 form carried in invoiceData.
The returned string is exactly what must be hashed for the request
signature, which is why encoding and hashing must never be done from two
separately serialised copies of the same invoice.
Serialise an invoice to the base64 form carried in
invoiceData.The returned string is exactly what must be hashed for the request signature, which is why encoding and hashing must never be done from two separately serialised copies of the same invoice.