Let's take an exmple of a 30% advance payment.

Such payments can be processed in the following way:

1. Create a single project and immediately invoice it, but add notes about the payment being split into 30% advance and 70% final.

2. Once the advance payment is made, create a new Payment in TO300 for the sum and link it to the invoice. This way the invoice will have 70% of its balance "due".

3. When the final payment arrives, link it tothe same invoice.