how to use Promo Code Text box.

hello,

 

how to use text box for promo code in c#.?

 

 Note:- we are mention admin panel promo code "20% off discount on purchase of $100 or above."  and coupon code is like"20Vale".

            but user are $1 to $99 not applied and $100 or above applied code. most think are user applied code but remove any product on page then code automatically remove. Testing Part

 

Thank You.