I recently signed up for a Chase Visa CC that earns miles on United. Chase sent me a voucher for $50 to be used when buying United tickets. Yesterday I priced out LAX-DEN for $179.40 ai. I figured I could use the voucher to get $50 off, but after applying the voucher the price only dropped to $153 ai. Why not down to $129? I'm not complaining, because it is free money, but if anybody knows why this happened I am interested to find out.