Sorry for the delay in responding, to get the 50 credit, [i'm sure there is an easier way, but this worked for me] use the box box on the main page and put in any prentend flight as if you were checking on prices, etc. when the next screen comes up you will see the 50 credit offer on the top of the page.
hope this works for you. $35 does not seem like a bad deal for 21k miles