We can pull up and customize the Transaction List by Customer report to get the data you need, trocky. I'll guide you on how to do this below.

QuickBooks Desktop (QBDT) offers various reports tailored to your business needs. In your situation, you can customize the Transaction List by Customer report to get the total payment of the invoice for a specific representative and month. Here's how:

1. Run the Transaction List by Customer report from the Reports menu's Customers & Receivables section.
2. On the report window, select Customize Report.
3. In the Display tab, set the Report Date Range and display the Rep column in the Columns section.
4. Go to the Filters tab.
5. Choose the Transaction Type filter and select the Multiple Transaction Types option.
6. Select Invoice and Payment, then click OK.
7. Click OK to close the Modify Report window. 

Once you're done, you'll want to memorize the above-mentioned report to save the same settings for future use. 

Also, many companies pay commissions to sales reps based on Gross Profit rather than the gross of the sale. This enables them to maintain profitability on an item if it is deeply discounted. To create a report for this, you can check out this article: Customize customer, job, and sales reports in QuickBooks Desktop.

Please keep in touch whenever you have other reporting concerns or issues about managing sales reps' transactions in QBDT. I'll get back to you right away to assist you further.