I find with these types of customers it’s always easier to just ask them to save files locally and grant me privileges to read the data. Sometimes they’ll be on Google, Dropbox, Microsoft, etc and I also run a SFTP for this in case they want to move them over to my service.

Then I either batch/schedule the processing or give them an endpoint to just to trigger it (/data/import?filename=demo.csv)

It’s actually so common that I just have the “data exchange” conversation and let them decide which fits their needs best. Most of it is available for self service configuration.