# Saturday, September 3, 2016¶

## Prepayment invoices¶

I worked on #1059 (continuing from Monday, August 8, 2016). It is almost done, but I get an error:

EvaluationError: Error while evaluating the expression
"jinja('sales/VatProductInvoice/trailer.html')" defined in the
"from" part of a statement. TypeError: unsupported operand type(s)
for *: 'Decimal' and 'float'


The trick to avoid this error (without adding Decimal to the default context of every parse operation) is:

Prepayment <b>30%</b> ({{(obj.total_incl*30)/100}} {{obj.currency}}) due on
<b>{{fds(obj.due_date)}}</b>, remaining
{{obj.total_incl - (obj.total_incl*30)/100}} {{obj.currency}}
due 10 days before delivery.


Change in database structure for PaymentTerm : The printed_text field must be a BabelTextField (i.e. separate for each supported language).

And then I added the last piece for this ticket: a new field payment_term per course which makes it possible to say that all enrolments to a given course get a given payment term.

In summary, Lino use a rather simple approach to handle prepayment invoices: only the global amount and the final due date is stored in the database, all intermediate amounts and due dates are just generated in the printable document. If you use different prepayment formulas, you define one PaymentTerm for each of them (and take care to configure your printed_text field).

I finished by adapting the test suites in Lino Voga, Lino Welfare and Lino Così.