# File upload

This method allows uploading a file. The file is sent as `multipart/form-data`, using the `file` field.

On success, the hash of the uploaded file (`externalFileHash`) is returned, which is later used to attach the file to transfer documents (the `AttachmentIds` field).

Allowed extensions: `docx`, `docm`, `dotx`, `dotm`, `docb`, `xls`, `xlsb`, `xlsm`, `xlsx`, `jpg`, `jpeg`, `png`, `ppt`, `gif`, `txt`, `pdf`, `zip`, `rar`, `tar`, `gzip`, `ico`, `dat`, `csv`, `xml`, `enc`, `svg`.

For a disallowed extension or a missing file, the HTTP status code `400 Bad Request` is returned with the message `File extension is not allowed`.

## Parameters

- `file` — file, required

  The file to upload. Sent via the `file` field of the `multipart/form-data` form.

**FORM-DATA**

```api
POST api/files/upload
Content-Type: multipart/form-data
```

```
file: (binary)
```

## Returned parameters

- `externalFileHash` — string

  A unique hash of the uploaded file. Used in the `AttachmentIds` field when creating a transfer document.

**JSON**

```json
"sample string 1"
```