Quantity discounts have a few limitations to keep in mind when you create a campaign.
1. Automatic discounts are limited in number
Shopify allows up to 25 active automatic discounts per store, and quantity discounts count toward this limit. The limit is shared by all your discount apps. If you've reached it, new campaigns won't activate until you deactivate some automatic discounts.
2. Quantity discounts always stack with sale prices
The discount is calculated from the product's current price, so a product on sale gets both discounts. To keep a quantity discount off sale items, exclude them by a collection, a tag or a vendor.
3. Whole products only
Currently, a quantity discount applies to whole products: there's no way to select single variants as targets or exclusions.
4. Collections must be available on the Online Store
The table on the product page can only check collections that are available on the Online Store sales channel. If a collection isn't available there and you set it:
As a target: the table won't appear on the pages of its products, but the discount still applies in the cart and at checkout.
As an exclusion: the table may still appear for its products, but the discount won't apply in the cart. Thus, customers might see a discount they won't get.
To avoid this, use collections that are available on the Online Store, or target and exclude by tags or vendors instead.
5. Gift cards are discounted too
Shopify treats gift cards like any other product. If a gift card is among your campaign targets (for example, when you target a vendor or a tag), it gets the quantity discount. Exclude gift cards if you don't want that.
6. Up to 10 tiers
A campaign can have up to 10 tiers. The first tier starts at 2 items or more.