The coupon should be valid. Amazon sometimes has glitch with the coupon codes.
I would suggest you log off Amazon, close out browser, open a new browser, login Amazon, then try the code again.
You may need to delete all the cache data in the browser to make it work.
Other customers was able to apply the code when they switched to another device or different browser ( Internet explorer to Google Chrome).
If it doesn't work, please reply us back.
The Smiley Daisy Team