Prepayment

[Sjoerd]

Occasionally I require a deposit to start an assignment. How can I subtract and specify such a deposit or prepayment from the total amount due using the invoice module?

[Adam]

While you cannot create the Invoice until you have item, you can enter the Payment.  You would just enter the payment as you normally would, but you would not do the second Apply step.  After you have done the work, then create the invoice.  Email it to yourself and mark as Billed.  Then you can apply the payment and generate the invoice again and it will show the amount minus the payment.  If you want, you can skip the step of emailing to yourself by going into the Manage Invoices, select the invoice and change the status from Pending to Billed and then apply the payment.

[Sjoerd]

I understand, but I would like to make the prepayment visible on the invoice. Also, if we for instance have to make a correction by subtracting an amount from (a next) invoice, we want to show that on the invoice.
In other words: it would be nice to enter a negative expense amount ("discount").

[Adam]

Payments do show on the invoice.  After you have "Applied" the payment, just regenerate the invoice and you will see it and the adjusted total.

We do have a "Discount" option on the Invoices as well.  In the Extra's section, just choose Discount and set the Discount Type (percentage or amount) and then enter the Amount.  One important note is that discounts are taken before Taxes, so if you are discounting your invoice, that is a good way to do it.

As far as payments go, you can Apply a payment to one or more invoices.  So it could pay two, three or more different invoices.