Customer Metafields?

I have been trying to use the standard Shopify API to add a new metafield set to existing customer records. I can inspect the customer info before the JSON update command is issued. And the new metafield appears in there. But the JSON command doesn't show the metafield set being passed along.

Does your project allow for customer metafields to be managed and manipulated? From my Googling around most of the documentation and practical applications of metafields revolve around the products and not the customers.