Anyone good at Promo codes want to take pity on me?

Hey y'all--I am having the worst time setting up a promo code.  Basically, we have a performance that we would like a promo code to trigger a $10 ticket (or $2.00 off $12.00) but I just can't get it to work.  Is it better to use pricing rules or offers for this?  Or are they all tied together?  Right now I get this error message when I put in the promo code:

Does anyone have fail-safe web promo instructions?  I'm literally losing my mind because I've done these before and they've been fine--any help would be much appreciated!

-Olivia A.

ppk3pe@virginia.edu