That's a common issue with messaging systems. When you upload a file, it's stored on the server temporarily to attach to the message. But downloading it later isn't always straightforward because the server might not retain the file after the message is sent.
One solution could be having a designated storage area where uploaded files are permanently stored, accessible via a link in the message. This way, users can download the file whenever they need to, even after the initial message is sent.
Hope that helps clear things up!