How to allow stacking multiple coupons for Shopify

While creating an Offer or Redemption, and choosing your Shopify Ecommerce as a location, you will then be able to choose a Combination.
The options are:
Product discounts
Order discounts
Shipping discounts (will not show when you have Free shipping selected)
For Pay with points and Pay with credits stacking coupons, you can go to Settings, Apps and Integrations, Shopify Configuration, and scroll down to the Earning & Redeeming section in order to be able to choose the Combinations.
Save.

Using Kangaroo along with your Shopify Integration, will allow your customers to stack multiple coupons at the same time.