>read CSV file from another third-party
Generally, if you're getting a CSV file from a client that indicates to me that theres a good chance they're exporting info from their systems and sending you the CSV.
Have you considered developing a client facing API that can be used to send and digest data?
We have, but that's not something my team (actuarial) can accomplish without help/blessing/oversight from IT.
I don't know all the details but we do have connections to some of our MGAs through XML dumps or perhaps real-time feeds (I'm doubtful). But that data is often missing some of the details as I need. It's useful for policy admin - not for all the other stuff.
We've also explored portals but those are fraught with concerns about double-entry.
Have you considered developing a client facing API that can be used to send and digest data?