Created a request

Observe in the Budget tab, that the budget is in account 63000:

On the Budget screen > Purchasing Expenses node, add Amount $12,000.00 to Account 63000:

On Release Budgets screen, click PROCESS ALL to get the budget released.

To get the Amount Spent field to populate, create a Request for a Non-Stock Item.

 - On the Non-Stock Item screen, change the Expense Account to 63000:

Request looks like this:

Create Requistion:

View Bidding, Complete Bidding

Create Purchase Order

Place PO on Hold

Add Discount to line

Approve:

Enter Purchase Receipt:

In Other tab, open the IN document:

On the Receipt, open the Batch Nbr.:

Observe the discounted amount $490 hit account 63000, not $500 from the Request:

Back on the Request > Budget tab, observe $490.00 has populated Amount Spent: