woocommerce_invalid_shipping_item error when trying to create an order via API

I am following the API at http://woothemes.github.io/woocommerce-rest-api-docs/#create-an-order but I get an woocommerce_invalid_shipping_item error when trying to create an order. I confirmed that flat_rate was enabled. What would cause this error?

https://wordpress.org/plugins/woocommerce/