Hey @primrosehill, hope you’re well, I just wanted to check in here!
Zapier will only be able to work with apps and devices that have an API that can send or receive data. Since the POS is backing up the data to a local machine, you would need to set up something like your own local API server that would serve up the file to DropBoxes API.
I did some Googling and I found a GitHub repo for a simple python script for uploading a file to Dropbox: https://gist.github.com/Keshava11/d14db1e22765e8de2670b8976f3c7efb
I have not reviewed the code in the above repo and do not endorse it’s developer, but it can serve as an example for you to get started with a local script for uploading files to Dropbox.
I don’t recommend setting up custom scripts unless this is something you’re familiar with and can review the source code personally for any potential issues regarding security or privacy.
I’m also going to move this over to our Webhooks and Code section in case anyone else may have some solid insight into this workflow for you. :)