This is a low level function that only works on attachments retrieved with gm_attachment().
To save an attachment directly from a message see gm_save_attachments(),
which is a higher level interface more suitable for most uses.
Examples
if (FALSE) { # \dontrun{
my_attachment <- gm_attachment("a32e324b", "12345")
# save attachment to a file
gm_save_attachment(my_attachment, "photo.jpg")
} # }