Select field mapping

{
  "core": {
    "key": "acf_select_field",
    "name": "ACF Select Field",
    "is_list": false,
    "is_required": false,
    "need_internationalization": false,
    "min_list_length": 1,
    "max_list_length": -1,
    "field_type": "choice",
    "source_id": null,
    "source_metadata": "{\"is_custom_post_type_field\": true}",  // It is important to identify source_metadata as custom field
    "order_index": 0,
    "help_text": null,
    "editor_metadata": null
  },
  "choices": {
    "A": "A",
    "B": "B",
    "C": "C"
  },
  "display_option": "dropdown",
  "default_values": ["A"]
}