We’re having a similar issue, our API won't let us set a shipping address. There is an option to change the shipping address option (like the dropdown on BC). Here's what it says if I set it to something different to what it should be:
not an option. The existing options are: Default (Sell-to Address),Alternate Shipping Address,Custom Address
But when set to Custom Address, it still won't let us use a custom address!
Property \"Editable\" for Ship-to Name is invalid. Expression: [p42ShipToOptions = p42ShipToOptions::\"Custom Address\"]
Anyone else experiencing this?