How can I set up an assignment to apply a client discount to their invoices?

To set up a client discount you will need to create a specific discount rate code in Rate Code Entry. You can add relevant description to the rate code, eg. Discount, and importantly set the Rate Code Type to On-Cost & Commission 

With the discount rate code setup, you will now need to apply the discount from the On-Cost & Commission section of the Assignment Entry. From here you need to select Add on-cost & commission.

*The Discount field in Client Entry is not related to the invoice*

Now you must select the Discount rate code from the On-cost & commission rate code drop down menu, and then choose Client Discount from the On-cost & Commission Type, as shown below. Then select the Add rule option

Now you must select the Discount rate code from the On-cost & commission rate code drop down menu, and then choose Client Discount from the On-cost & Commission Type, as shown below. Then select the Add rule option

Next select Update to add the discount to the assignment. The discount will then be applied to the bill side of any timesheets for this assignment, as shown below

This discount on the timesheet will then be applied to any invoices that are generated, with a separate line on the invoice indicating the discount that has been applied