Currently, there is no built-in Customer Sales Detail by the Sales Rep report to pay commission in QBO at this time.
The workaround in QBO is to use one of three available custom fields on the sales forms (invoice and sales receipt) for Sales Rep (as a text field). And then you can run the standard Sales by Customer Detail Report, and filter Group by Sales Rep. Since this is just a text field so you will need to assign sales rep every time you create an invoice or sales receipt.
With QBO Advanced version, you can assign Sales Rep at the Customer Information level but on other plans, such feature option is not available.
