I am in the same boat, but only when trying to apply WestJet points. I kept getting error messages (thought it was the card at first so I tried another one, same problem).

Then by mistake I made the purchase without applying WestJet points, it went through. (I immediately cancelled, so no big deal.)

Tried again with WestJet points, no dice. I am going to call in to get an agent to force the payment through which I understand they can do. I expect to not have to pay any phone booking fee given that the website is clearly messed up.