def body(id, t)
      [id, t.id, t.date.utc.iso8601, t.amount.to_i, t.prefix, t.bnf, t.details].join(' ')
    end
def body(id, t)
      [id, t.id, t.date.utc.iso8601, t.amount.to_i, t.prefix, t.bnf, t.details].join(' ')
    end
Create the body for transaction signature.
 +id+:: The paying wallet ID
 +t+:: Transaction, instance of Txn