It only takes one bad experience for a customer to abandon his/her cart, potentially never to return. And discounts can be a sensitive area as shoppers get excited for the savings, but become frustrated if the code does not work as expected or has already expired. Avoid all that by being friendly and proactive.
The other key to a great experience is consistency. If a shopper is offered multiple discounts in short succession, the experience no longer feels personalized and customers think a better offer will come if they wait or try to game the system. Leading with your best offer and presenting it consistently across channels will get customers to convert faster and leave them feeling like they got the best deal possible.