Add a fulfillment Service for each unique vendor/shipping rule.
You can create as many “Fulfillment Services” as you like by going to the last section of the Shipping section in the admin.
When you create a fulfillment service you just need to provide a Title/Label and a email address. (If you want an order notification email sent to the vendor, you can include their email. If you don’t, just put your own email address or a dummy one.)
Any custom fullfillment service you create will be made available the next time you open the app to create a shipping rule for it.Read more about custom fulfillment services
Associate your products/variants with the fulfillment services you’ve created.
Single Variant Products
Multiple Variant Products
Open the app and set-up rules for each Fulfillment Service/Vendor
Put together some test orders and proceed to the shipping portion of the checkout to verify that the rules are working properly.