Hey @create yotpo birthday flow 

Can you share a little more on what your goals are and what you are trying to accomplish by offering a discount in your flows?

to make someone purche when he add to cart/check out strat

Great question @create yotpo birthday flow ,
One of my favorite things about Klaviyo is that you can test this all out within the flows to see what is better for your brand. We’ve tested out various offers from % off, $ off, free shipping, to no promotions at all. It is very client specific in terms of what the winning result is. 

We have found the best luck with providing discounts in the welcome series and abandoned cart emails.  I would offer a different code in each email or do a dynamic code to make it easier to track which flow is doing the best, but keep the discount level consistent.  Hopefully that helps!