curl --request POST \
  --url http://localhost/api/v3/profile/custom-attributes/batch.json \
  --header 'Content-Type: application/json' \
  --data '
{
  "profiles": [
    {
      "profile_id": "<string>",
      "custom_attributes": [
        {
          "namespace": "<string>",
          "handle": "<string>",
          "value": "<string>",
          "type": "<string>"
        }
      ]
    }
  ]
}
'

{
  "data": {
    "message": "<string>",
    "batch_id": "<string>"
  }
}