Upload file for Task additional File field

Work with a Task. Upload a file into a File-type additional field of a Task.

This endpoint exists because PUT requests do not support file uploads in PHP, so file uploads to additional fields require a separate POST {id}--upload request with multipart/form-data.

The form-data field name must follow the format additional_attributes[<field_name>], where <field_name> is the technical name of the configured File-type additional field.

File constraints: max 50 MB, extension validated against the allowed file types (see Allowed files types).

After a successful upload, the file value can be retrieved via GET on the same Task — the additional_attributes.<field_name> object will contain api_url, web_url, filename and download_link. download_link is an absolute URL with hash and time query parameters that authenticate the download for a limited time, so it can be opened directly without a session cookie or access token (useful for previews on mobile clients).