AttachmentIn

One message attachment: exactly one of an owned file_id or inline base64 file_data.

file_idstring<uuid>nullable

Identifier of an owned file created via POST /v1/files. Provide exactly one of file_id or file_data.

file_dataFile Datanullable

Base64-encoded file bytes (a data:…;base64, prefix is accepted and ignored). Provide exactly one of file_id or file_data.

AttachmentIn

{
  "file_id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
  "file_data": "string"
}