To set up payment terms in Odoo 16, you can follow these steps:

Go to the "Accounting" module and click on "Payment Terms" under the "Configuration" menu.

Click on the "Create" button to create a new payment term.

In the "Payment Terms" form, fill out the required fields such as "Name" and "Active."

Under the "Terms" tab, you can specify the payment terms for your customers. For your requirement, you can create two lines with the following details:

Line 1: Discount (10%)
Type: Percentage
Value: 10
Number of Days: 0 (immediate payment)

Line 2: Net (50% now, 50% in 45 days)
Type: Balance
Value: 50
Number of Days: 0
Second installment: 50
Second due date: 45

Save the payment term.

Now when you create a new invoice, you can select this payment term to apply the discount and set the payment schedule as per your requirements.

For the configuration see also the new tutorial-video: https://www.youtube.com/watch?v=2BF4xkMlSHA&t=1s