This is strange. That is not an invalid code as it made the discount, and I just tried it on 2 different computers and it worked. It also works with all upper case and all lower case. I tried misspelling it and it just did not apply (got the error where you input it)

I checked if the firewall was blocking something, and it is not.

Can I ask you to try it again and if it doesn't work, put up and image of your entire screen? We can take this to email if that would be easier.

Thanks!