Reality XP bundle discount coupon HOW?

I am a new xplane user and just tried buying the GNS 530/430 bundle.  Maybe it's just me, but I could not figure out how to apply the coupon.  While strugglilng with that problem, somehow the purchase went through for the 530 only at $49.95.  I would have like to get the 430 as well for $10 more with the coupon, but it just would not work.  Applying the coupon was a needlessly opaque and arcane process.  Is this by design?  I hesitate to buy more Reality XP products until I can get this sorted out.