If you're new to reviewing on Google Play, 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 Google Play heading. It should take you directly to the book's review page where you can leave your review.
On Google Play's website, click on "Write a review".
Fill out Google Play's form to complete your review 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 Google Play section.
Scroll down to the bottom and click the "save" button.