title: Magento 2.1 - Cant update Customer Custom Attribute via REST
body: <p>I am trying to update a Custom Attribute in a Customer</p>
  
  <p>However the PUT request is not working...</p>
  
  <pre><code>{
  "customer":{
      "id":111,
      "group_id": 1,
      "email":"abcd@com",
      "firstname": "first",
      "lastname": "last",
      "taxvat": "123456789",
      "website_id": 1
  },
  "custom_attributes": 
  [
      {
          "attribute_code": "customer_erp_id",
          "value": "66666"
      }       
  ]
  </code></pre>
  
  <p>}</p>
  
  <p>Endpoint ..../rest/V1/customers/111</p>
  
  <p>There's an existing post <a href="https://stackoverflow.com/questions/46254405/magento-2-rest-api-customer-custom-attribute">Magento 2 REST API Customer Custom Attribute</a>
  which seems to conclude that this is not possible</p>
  
  <p>As it is a bit old I was wandering if anybody was able to get this working...
  Thanks</p>