Promotional Code Not Working

[pittsburghhatz]

Hi - I have an email saying that I can get $6 off by using promotional code MY6OFF at checkout.  I just tried to use it at checkout and it's telling me "Looks like that's the wrong code. Please double-check and try again."  I cannot seem to get it to work.  Please help me out - I clicked BUY IT NOW, so it's forcing me to pay.  Thank you.