This is an accepted solution.
Shopify doesn't have any inbuilt option for this.
However, you can use Voila - Coupon Discount on Cart Shopify app to create:
i) A coupon code field where your customers can apply a discount code on the cart page itself before going to the checkout step.
ii) Now the coupon code field is much more effective in reducing cart abandonment if you also show selected coupons on the cart page. Your customers will be delighted when they get a surprise discount and this reduces cart abandonment.
With Voila you can also show selected coupons on a Pop-up which works like this:
Let me know if this helps.