sorry for the delayed answer. You need to add a payment to the invoice. Select the invoice and choose the info tab. Click "Add Payment" and add a new payment.
Hi, there is a filter for payments in 2.0.7 which is unfortunately applied to the entire application. This is a bug and we are sorry for that. Here is a fixed version http://www.kedisoft.com/dl/totals/Totals-2.0.8b3.zip we will release 2.0.8 very soon. In the meanwhile please use this one.