But the t-shirts vary in price so I’m not sure what the discount would be if they selected a $34 shirt, a $36 shirt. I would want them to be able to select 4 shirts and when they get to the cart, it auto goes to $100. Does that make sense? If you look at this product page and go through the flow, it does it perfectly https://www.marinelayer.com/collections/guys-3-for-100..
For an automatic discount to work, customers must add all eligible items to their cart. This means both the items that they are purchasing and the free item. This means that you must communicate to your customers that if they would like to make sure of this promotion, they must add the free item to the cart themselves.
You can create Shopify Automatic discounts but only a discount code will apply moreover if you take any third app party app it won’t support the Shopify Automatic discount.
I suggest you can take the help of third party app with many feature. Here are few third party app which increases your store sales.
Kart Discount App:
Easy to setup the discount field on the cart page. Show Discount Field on Cart Page and Side Drawer,
Features:
1.Stack Discount
2.Multiple Automatic Discount
3.Discount Finder
Free Shipping Estimation
Multi- Currency Option
6.3rd Party app compatibility and much more
Discount Reminder
Key features of the app:
Robotized notices: Allow your clients to buy in for items and get advised consequently when you bring down the cost and spot items on sale.