Hello! My question is: how to resolve the problem collecting a flat shipping fee using Collective products on International Orders with multiple vendors in a single order?
I have a flat fee set for International orders and I noticed that if the customer adds a Collective product among Non-Collective products, at the checkout there is a message to remove the Collective item because it can’t be shipped to that address.
I’d love to find a solution because that’s what is preventing us to sell more Collective products to avoid customer confusion. Right now and recently I just added a couple of vendors to test it live. But International customers will not be able to purchase if adding other items. Which is a problem because our store sells multiple vendors in a single order a lot of times, both domestically and internationally.
Looking forward to hear your feedback and input. Thank you! 
Hello @BellaBella
This is expected behavior when Shopify Collective items and normal shipping profiles are mixed, particularly on international rates. Collective products have their own fulfillment requirements and Shopify treats them as incompatible with certain shipping rules if you use them together in one checkout.
The cleanest solution with “least friction” is to have the shipping logic separated per product type. Make a separate shipping profile for Collective items with its own international flat rate, and make sure all Collective products only belong to that one profile. This stops Shopify from attempting to merge the conflicting rates within a single cart.
For your purpose, if you really need mixed carts, a more scalable approach is a shipping rules app that can combine rates from different profiles and enforce a single blended flat rate at checkout, and does not show the “remove item” error.