Create and verify your first split

Start without MSI so the first result depends only on vendor grouping. Add source routing after the basic flow works.

Prepare the vendor attribute

The vendor attribute is the product attribute that identifies the supplier or fulfilment owner of each item. The extension ships with manufacturer as the default — reuse it or create your own attribute (for example supplier) and select it in the configuration.

Open Stores > Attributes > Product.
Create or choose a Select attribute such as Supplier.
Add two realistic options, for example Northstar Components and Alpine Workplace.
Add the attribute to the product attribute sets you use.
Assign one option to each of two simple products.

A Multiselect attribute is also supported, but its complete stored value set is treated as one group. It does not copy an item into several orders.

Use a conservative first configuration

Enable Order Split.
Select the supplier attribute.
Set missing vendor, disallowed payment and missing shipping behavior to Block Checkout while validating data.
Set Use MSI Source Selection to No — the shipped default enables it, which would split by warehouse source in addition to the vendor attribute.
Allow one payment method that is safe in your local demo.
Set discount, shipping and tax to Recalculate Per Split Quote.
Enable the checkout notice.

Submit the cart

Add both products to one cart and complete checkout with the allowed payment method. The success page should show both order numbers.

Magento checkout notice explaining that products from multiple suppliers will create separate orders

One customer cart is grouped by the configured supplier attribute. Each group becomes its own quote and Magento order, while the split registry keeps the related order numbers together for the success page and Admin review.

Magento checkout success page listing the two order numbers created from one supplier-based cart

Verify the result

Check all of the following:

Sales > Orders contains two orders.
Each order contains only the product assigned to its supplier group.
The totals and shipping method are valid on both orders.
Each order history contains a non-customer-notified split comment.
Sales > Orders > Order Splits contains one group with links to both orders.
The customer order view links the related split orders.

If Magento creates one order, use Common issues before adding MSI or proportional totals.