Question

I want to apply discounts in this scheme like:
a. if 3 or more product in cart then 10% discount.
b. if 5 or more product in cart then 15% discount.
c. if 10 or more product in cart then 20% discount.

I created all three discounts and added them in app but only one discount works at a time on cart page here is screenshot:

Answer

Try to put the rules in the opposite order, from the biggest discount (biggest rule) at the top to the smallest at the bottom.