According to the API information you can add a message with the file.
type=file
file_name - The name of the file.
file_type - The MIME type of the file.
file_url - The url where the file can be downloaded.
body - (OPTIONAL) A message to go with the file.
are you able to add the body bit so it can be passed?
According to the API information you can add a message with the file.
type=file
are you able to add the body bit so it can be passed?