If you're new to reviewing on Smashwords, follow these steps to leave your review on their website and prove to Booksprout that you've completed your review.
Click on the "Leave Your Review" button just under the Smashwords heading. It should take you directly to the book's review page where you can leave your review.
On the Smashwords website, click "Write a review" (it's small and just above the list of other people's reviews).
Fill in the required information in the form that pops down and click "Submit."
Once submitted and you can see your review on their website, come back to Booksprout and click the "Yes, I left my review" checkbox in the Smashwords section.
Scroll down to the bottom and click the "save" button.