Unable to use 50% discount code for THX Spacial

I have been using the 7.1 Surround Sound app for my pair of Razer Blackshark V2 X headphones.  I recently saw that there was a 50% discount code for THX Spatial Audio.  I have tried to enter it in the THX Spatial Audio software and in the apply promo code when checking out.  It will not work anywhere I input it.  Am I doing something wrong?  Is the 50% discount no longer valid?  Thanks in advance for your help.