When you click on "Save & Send Test", the Communications Center does not have a real customer order from which to pull in details. When sending the test message, we populate the order details with fictitious content, including a fake Order Id, product, etc. These emails will NOT actually be sent to your buyer.
Due to this, you will be redirected from the page where you can leave Seller Feedback or a Product Review. You may receive an error like "We experienced a temporary problem in our systems. Please try again in a few minutes." However, you should be able to tell that you are on the right page. You will be on Amazon's site where you see a subtitle like "Leave Seller Feedback", "Your Reviews", or "Write a Product Review".
When the message is set to Active, they'll begin sending to your customers containing accurate information and functional links.