How to require Product B when a customer buys Product A

Use Purchase combination rules → Buy together and place Product A in the Trigger group and Product B in the Required group. When the cart contains A, the rule requires B as well. You can also require matching quantities or a specified ratio.

Create the A-plus-B rule

1. Open Combinations from the app navigation, create a rule, and choose Buy together.
2. Name and activate the rule. Under Groups / targets, select Product A for the Trigger group and Product B for the Required group. Check that the groups have not been reversed.
3. Set Buy together mode to Presence only: whenever A is present, at least one B is needed. Use Same quantity for a 1:1 mapping, or Ratio to enter trigger and required unit quantities.
4. Configure the warning trigger, customer tags, and active times if needed. Edit the Buy together message so the customer knows which item to add.
5. Save and activate the rule. For checkout blocking, confirm both rule-level and shop-level Checkout Validation are on and the all-customers bypass is off.

Compare three carts

In Presence only mode, A × 1 without B should show the missing-item message and fail checkout validation; A × 1 plus B × 1 satisfies this combination rule. With B × 1 alone, the Trigger group is absent, so this rule does not apply. Adjust quantities in the editor Preview, then verify in the real storefront and checkout using the storefront test guide.