You will also need to contact Shopify and ask them to disable multi-origin shipping on your store for you, otherwise Shopify will always obtain separate rates for each unique location when customer purchase from multiple suppliers at the same time, and then try and combine the rates, however the way Shopify combine the rates is by name only, which means it may not work correctly. Disabling multi-origin shipping will prevent this and still allow you to use multiple locations to set your inventory.
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