Update Form Api not allowing to reorder the fields

As the title says, I am trying to update an existing form through the API and I am getting the following error 

{"code":"VALIDATION_ERROR","description":"The payload is invalid.","details":[{"code":"WRONG_TYPE","description":"should be object","in":"body"}]}

Here is an example of the post data I use to create the form

data = [
   'title' => 'title',
   'type' => 'form',
   'fields' => [
       [
           'properties' => [
               'description' => 'brief',
           ],
           'ref' => 'campaign',
           'title' => 'campaign',
           'type' => 'statement'
        ],
        [
           'properties' => [
               'description' => 'details',
           ],
           'ref' => 'event',
           'title' => 'event,
           'type' => 'statement'
        ]
   ],
   'workspace' => [
       'href' => 'https://api.typeform.com/workspaces/{href}
   ]
];

And this is the data I use to update it

 

data = [
   'title' => 'title',
   'type' => 'form',
   'fields' => [
       [
           'properties' => [
               'description' => 'brief',
           ],
           'ref' => 'campaign',
           'title' => 'campaign',
           'type' => 'statement'
        ],
        [
           'properties' => [
               'description' => 'new field',
           ],
           'ref' => 'newfield',
           'title' => 'new field',
           'type' => 'statement'
        ],
        [
           'properties' => [
               'description' => 'details',
           ],
           'ref' => 'event',
           'title' => 'event,
           'type' => 'statement'
        ]
   ],
   'workspace' => [
       'href' => 'https://api.typeform.com/workspaces/{href}
   ]
];

As a side note, something I discovered is that if I add the new field below the last one, it works, is there any way I can sort the fields so I have the newly added fields where I need them?

​​​​​​​Thanks in advance!