The Coupon code it's not a Serial Number that can be used to activate the product, it's something that you can only use to get a discount when purchasing, and by purchasing you'll get an order receipt which contains your Serial Number so, once you purchased the scenery, the Coupon code is not needed anymore.
If you lost your purchase receipt, you can retrieve it another copy as explained on the manual ( fsdt_install_guide.pdf), on the FAQ page:http://www.fsdreamteam.com/faq.html
I have lost my Email receipt, how can I reactivate my product ?
You can go to Esellerate support site here:http://store.esellerate.net/support
You can retrieve your Order History, by inserting the email you used to purchased the product, then press the "E-Mail Order History" button. Having your Order, will allow to use the server-assisted Reinstall. If you want to know your Serial Number, insert your Order Number and Email, then press the "Submit" button on the Esellerate support site: this will enter inside your Order Page, with option to see your original Email Receipt, that contains also your Serial Number.
and on the forum here:http://www.fsdreamteam.com/forum/index.php?topic=649.0
If the Esellerate store doesn't find all your purchases, it means you have purchased with a different email, if your old email it's not accessible anymore, you should contact us via email, telling which email you used for the original purchase and what is your current email, so we can update your order.