Arghh... I figured out how to use the $50 off, you have to enter the cert number and redemption code before the flight search.
BUT...
When you click through that way, you don't get the option to pay with certificates. So it's $50 off, but you have to charge the rest.
So it is one or the other, $50 off ..OR.. pay with e-certs
<OFF TOPIC>
Has anyone ever found a way to use e-Cert to renew Sky Club?
</OFF TOPIC>