I have been working on this for some time (Months off and on) but have gotten no where.
I have seen the same answer on multiple thread by @Prakash but they seem to be missing something - possibly because they reference a v6.1 manual
https://www.odoo.com/forum/help-1/question/how-to-configure-ecommerce-shop-coupons-56723.
I have tried setting up the price list and know that they work as I am using them for other aspects of my sales but there seems to be no way of adding a coupon / Promotion code to them.
I've tried using then name of the price list and price list variant as the coupon but neither work.
Would love to here from anyone who has successfully done this in V8 -
Infact I will Paypal you $10 if you help me get it to work - Promise
Tim