curl --request POST \
  --url https://sandbox.tight.com/v6/files \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "data": [
    {
      "description": "Q1 2024 invoice",
      "id": "fil_28868401",
      "entityId": "btxn_28868401",
      "notes": "Received from vendor on 2024-01-15",
      "date": "2024-01-15",
      "amount": 15000,
      "customData": {
        "internal_key": "some_internal_key",
        "some_other_field": 23434
      }
    }
  ]
}
'

{
  "data": [
    {
      "data": {
        "id": "fil_28868401",
        "entity": {
          "id": "btxn_28868401"
        },
        "description": "Q1 2024 invoice",
        "notes": "Received from vendor on 2024-01-15",
        "url": "https://cdn.sandbox.tight.com/files/fil_28868401.pdf",
        "date": "2024-01-15",
        "amount": 15000,
        "status": "ACTIVE",
        "customData": {
          "internal_key": "some_internal_key",
          "some_other_field": 23434
        }
      },
      "error": [
        {
          "message": "<string>",
          "param": "<string>"
        }
      ]
    }
  ],
  "error": [
    {
      "message": "<string>",
      "param": "<string>"
    }
  ]
}