How to Set Up Mixed Cart Orders for Preorders

Mixed cart orders occur when customers add both preorder items and regular in-stock items to the same cart. STOQ lets you control whether to allow or prevent this behavior. Restricting mixed carts can simplify fulfillment by keeping preorders separate from regular orders, while allowing mixed carts provides flexibility for customers who want to purchase multiple items together.

What Are Mixed Cart Orders?

A mixed cart order contains both preorder products and regular products in the same checkout.

Example Scenario

A customer adds:

• Product A (preorder, ships in 4 weeks)
• Product B (in stock, ships immediately)

If mixed carts are allowed, both items go through checkout together as one order. If mixed carts are restricted, the customer sees an error and must purchase them separately.

Why Mixed Carts Matter

Mixed cart orders affect your fulfillment workflow:

With mixed carts allowed:

• Customers can purchase everything in one transaction
• You may need to split shipments or hold the entire order
• More convenient for customers
• More complex fulfillment logistics

With mixed carts restricted:

• Preorders are always separate from regular orders
• Simpler fulfillment workflow
• Customers must complete multiple checkouts
• Clearer order management

When to Allow Mixed Carts

Allow mixed cart orders when:

• You want to maximize customer convenience
• Your fulfillment process can handle split shipments
• You use STOQ's split fulfillment feature for mixed orders
• Customers frequently buy preorder and regular items together
• You want to increase average order value

When to Restrict Mixed Carts

Restrict mixed cart orders when:

• You want to keep preorders completely separate
• Your warehouse cannot easily split shipments
• You prefer simpler order management
• Preorder items have significantly different shipping timelines
• You want to avoid customer confusion about delivery dates

Accessing Mixed Cart Settings

The mixed cart settings are located in the Limits section of the offer editor.

Navigating to the Settings

1. From your Shopify admin, open the STOQ app.
2. Click Preorders in the left navigation menu.
3. Click Offers to view your preorder offers.
4. Click on an offer to open the editor.
5. Click on the Limits section in the offer summary.

Configuring Mixed Cart Settings

By default, STOQ allows mixed cart orders. Follow these steps to restrict them.

Restricting Mixed Carts

1. In the Limits panel, locate the Mixed cart orders section.
2. Check the box labeled Don't allow mixed cart orders.
3. A Customize link appears below the checkbox.

Customizing the Error Message

When you restrict mixed carts, customers see an error message if they try to add a preorder item to a cart containing other products (or vice versa).

1. Click Customize to expand the error message field.
2. In the Mixed cart error message field, enter your custom message.
3. The field supports HTML for formatting.

Example Error Messages

Simple message:

Preorder items must be purchased separately from regular items.

Helpful message:

This preorder item cannot be added to your current cart. Please complete your current order first, then return to preorder this item.

With link:

Preorder items ship separately. Please <a href="/pages/preorder-faq">learn more about our preorder policy</a> or complete your current order first.

Explaining the reason:

To ensure accurate delivery estimates, preorder items must be purchased in a separate order from in-stock items.

Allowing Mixed Carts

To allow mixed cart orders:

1. In the Limits panel, locate the Mixed cart orders section.
2. Uncheck the box labeled Don't allow mixed cart orders.
3. Customers can now add preorder items to carts with other products.

Saving Your Changes

1. Click Save changes to apply the mixed cart settings.
2. The setting takes effect immediately for all products in this offer.

What Customers Experience

Understanding the customer experience helps you configure the feature appropriately.

When Mixed Carts Are Allowed

Customers can:

• Add preorder items to a cart with regular items
• Checkout with both types of products
• Receive one order confirmation for all items
• Expect different shipping timelines for different items

When Mixed Carts Are Restricted

If a customer has regular items in their cart and tries to add a preorder:

• They see your custom error message
• The preorder item is not added to the cart
• They must complete their current order first
• Then they can start a new cart with the preorder item

If a customer has a preorder item in their cart and tries to add a regular item:

• They see your custom error message
• The regular item is not added to the cart
• They must complete the preorder order first
• Then they can purchase regular items separately

Mixed Carts and Split Fulfillment

If you allow mixed carts, consider using STOQ's split fulfillment feature.

How Split Fulfillment Works

When split fulfillment is enabled:

1. Customer places a mixed cart order
2. STOQ automatically splits the order for fulfillment
3. In-stock items can ship immediately
4. Preorder items ship when ready
5. Customer receives multiple shipments

Configuring Split Fulfillment

Split fulfillment is configured separately in the Shipping section of the offer editor. See the "Split fulfillment automatically for mixed cart orders" article for details.

Recommendation

If you allow mixed carts, enable split fulfillment to:

• Ship in-stock items without delay
• Keep preorder items on hold until ready
• Provide better customer experience
• Maintain accurate fulfillment timelines

Best Practices

Follow these recommendations for effective mixed cart management.

Communicate Clearly

• Write clear error messages that explain why items can't be combined
• Include links to FAQ pages if you have detailed policies
• Use friendly, helpful language rather than technical terms

Consider Your Workflow

• Evaluate your fulfillment capabilities before deciding
• Test the customer experience from both perspectives
• Train your team on handling mixed vs. separate orders

Be Consistent

• Apply the same mixed cart policy across similar offers
• Communicate your policy on product pages and FAQ
• Set customer expectations before they reach checkout

Monitor Customer Feedback

• Watch for support requests related to mixed carts
• Adjust your policy based on customer needs
• Consider A/B testing if you're unsure which approach works better

Mixed Carts Across Multiple Offers

If you have multiple preorder offers, each can have its own mixed cart setting.

Scenario 1: All Offers Restrict Mixed Carts

• Customers cannot combine any preorder with regular items
• Customers cannot combine preorders from different offers
• Each preorder must be purchased separately

Scenario 2: Some Offers Allow, Some Restrict

• Behavior depends on which offer's product is in the cart
• Can create inconsistent customer experience
• Consider using the same setting across all offers for clarity

Scenario 3: All Offers Allow Mixed Carts

• Customers can combine any products freely
• Use split fulfillment to manage shipping
• Most flexible for customers

Known Limitations

The mixed cart feature has some constraints to be aware of.

• The mixed cart setting applies to the entire offer, not individual products
• Error messages are shown at add-to-cart time, not at checkout
• The setting does not prevent customers from placing separate orders for the same items
• Custom error messages support HTML but not JavaScript
• The restriction applies to the cart, not to draft orders created in admin
• If a customer has items from multiple restricted offers, they may need to place multiple separate orders

Troubleshooting

If you encounter issues with mixed cart settings, use this guide to identify and resolve common problems.

FAQs

Q: Can customers combine preorders from different offers?

A: If both offers allow mixed carts, customers can combine preorders from different offers in the same cart. If either offer restricts mixed carts, the restriction applies and customers see an error.

Q: Does the mixed cart setting affect existing orders?

A: No. The setting only affects new add-to-cart actions. Existing orders are not changed when you modify the mixed cart setting.

Q: Can I allow mixed carts but require separate shipping?

A: Yes. Allow mixed carts and enable split fulfillment. This lets customers checkout together while you ship items separately based on availability.

Q: What happens if a customer's cart becomes "mixed" due to inventory changes?

A: If a product in the cart changes from in-stock to preorder (or vice versa) after being added, the mixed cart restriction does not retroactively apply. The restriction only checks at the time of adding items.

Q: Can I customize the error message per product?

A: No. The error message is set per offer and applies to all products in that offer. To have different messages, create separate offers with different error messages.

Q: Does the restriction work with quick-add buttons on collection pages?

A: Yes. The mixed cart restriction applies regardless of how the customer adds items to the cart, including quick-add buttons, product pages, and any other add-to-cart method.

Updated on: 21/03/2026