def build_invoice
      InvoiceCollection.from_response API.post("#{invoices.uri}/preview")
    rescue Recurly::API::UnprocessableEntity => e
      raise Invalid, e.message
    end
def build_invoice
      InvoiceCollection.from_response API.post("#{invoices.uri}/preview")
    rescue Recurly::API::UnprocessableEntity => e
      raise Invalid, e.message
    end
Builds an invoice from the pending charges on the account but does not persist the invoice.
 Raises an error if it fails.

 @return [InvoiceCollection] The newly-built invoice that has not been persisted.
 @raise [Invalid] Raised if the account cannot be invoiced.