uploading a file

[jbonta]

Is there a way to send an image file without it being accessible via a server URL? I need to send private images, so it'd be more convenient if I didn't have to map it to a static resource URL on my web server. The API seems to allow it with filedata:
https://developers.facebook.com/docs/messenger-platform/send-messages/#file

To that end, is there a way to do so with saved assets/attachment IDs? Thanks!