Canyon promo code - where to enter

I have a promo code for 3 months free membership from Canyon.
When I go to promotions on my PC, enter the code and click “redeem”, it takes me to the next screen which aks for my $14.99 payment.

What am I doing wrong? I currently have a free trial and am a first time user.

Just to be clear, you are going here correct:

If that is the case you might want to contact Zwift Support: