If you haven't read our Upsells Introduction help doc, please check that out first to familiarize yourself with our Upsells feature.
If you haven't read our Course Affiliates help doc, that's a good one to know as well.
For a Course Affiliate to get credit for an Upsell, there's ONE simple step when placing an Upsell on a Payment Page you have to take.
THE ONLY STEP: When you're editing a Payment Page and you click the "Add Upsell Display" button, there's a checkbox to allow affiliates to earn a commission on the Upsell!
By checking the "Allow course affiliates to also earn commissions from this Upsell" option, the existing Course Affiliate commission percentage you set for your affiliate will be inherited during the checkout process.
#1 You've already added a Course Affiliate to your $75 Sourdough Bread 
Course (you can also add a Course Affiliate later on and as long as the "Allow course affiliates..." box is checked, you don't have to do anything else).
#2 The Course Affiliate gets a 30% commission for any customer they refer. This commission % ("Fee") is earned for the Course amount ($75) AND the Upsell amount ($30).
#3 Your Course Affiliate uses their affiliate URL from the email they received when you added them as an affiliate.
#4 When your affiliate generates a sale, they will get:
$22.50 for the Course (30% of $75)
AND $9 for the Upsell (30% of $30)
= $31.50 total to the affiliate (out of a $105 total purchase)
You'll get a "Course Sold" email notification listing the Course and the Upsell.
You AND your Course Affiliate will receive emails that the affiliate sale was made and how much of a commission (minus affiliate fees) was earned
#5 And that's it! 
You can see ALL of this information if you navigate to the Customer Profile of the customer who made the purchase via the affiliate.
