Routing every order to the right warehouse before ShipStation sees it

The problem

ShipStation decides where an order ships from based on what it receives. For products stocked in more than one warehouse, the brand wanted the warehouse chosen by where the customer lives: if the shipping ZIP code falls in a warehouse's area, that warehouse should get the line. Otherwise the order should go through untouched.

What we built

A small layer that runs before the order is sent to ShipStation. For each line it checks whether the product can ship from more than one warehouse and whether the shipping ZIP is in a warehouse's list. If both are true, it adds that warehouse's code to the SKU, so ShipStation routes the line to that warehouse. Everything else passes through unchanged.

• Built entirely on WordPress action hooks, with no changes to WooCommerce or ShipStation code, so updates to either do not break it.
• The SKU lists, ZIP lists and warehouse codes live on simple settings pages, so staff can change them without a developer.

Testing

The client ran a proper edge-case matrix: a matching product with a ZIP outside every area, a matching product with the other warehouse's ZIP, and a non-matching product with a matching ZIP. It found two small faults, a stray separator and one wrong code, which we fixed the next day. The client then confirmed everything worked "exactly the way it should".

Results

• Order lines routed to the right warehouse automatically, by shipping ZIP code.
• Rules the operations team can change themselves.
• No custom code inside WooCommerce or ShipStation to maintain.

Client name and site withheld at our discretion. Details are taken from the project record.