When discussing on Facebook Messenger, you can upload files and send them to the person you're discussing with. I'm actually developing a Messenger Bot (see documentation) and therefore, I'm trying to find the limits of this upload tool.
I found that it's not possible to upload files bigger than 25MB (I put here how I found this information).
However, I couldn't find for how long these attachments are available once uploaded? Indeed, Facebook Messenger is uploading the file on server and is sending a link to that resource in the communication. But I couldn't find if this link will be available forever or if access to it will be limited in time (and therefore, I guess the attachment would be deleted after this duration).
In order to get a response to my question, I uploaded a file and checked regularly its availability. Since I couldn't check every minute, I got a +/- 1 day precision but it seems that files stay available between 2 and 3 days.