magento 2 api rest billing address custom attributes not updating

{
"customer": {
    "email":"[email protected]",
    "firstname":"Roberto Carlos",
    "lastname":"Castillo",
    "storeId": 1,
    "websiteId":1,
    "gender":"1",
    "custom_attributes" : [
            {"attribute_code" : "foo", "value" : "bar" }
    ]
},
"password":"Test12345"