What are the best practices for discount promotion on web and mobile?

Question

Looking for the information of how to promote discount in web and mobile app experience, both for existing users who already made purchases AND for those who haven't yet. If you ran into any valuable researches or real use cases on this topic - please share.

Answer 1

1. In popup if the contents are more.
2. A stripe above the app ( if you give permission to close ).
3. A bar below the top bar or nav bar ( if you don't allow user to close it ).

Answer 2

Please provide more context for better understanding like at what stage these offers comes, is it after certain task user performed like signing in newsletter etc.

Though some common best practices are:

• Notification bar both on web and mobile works quite well, know it
  from experience. (Keep color contrast in consideration)

• Delayed popup at Product listing and description works too but keep it as minimum as possible.

• Discount coupon are highly effective on cart page as side banners and also reduce discount hunting and cart abandonment.

Here is research done about discount and its application by NNG

https://www.nngroup.com/articles/applying-discounts/