Options for SHARED text file for RW from VBA

My excel file VBA project successfully reads & writes data to/from a text file on our local network. It is used by multiple users within my company, RW to the same txt file on the network.

I've been asked to share the excel file with another company, who also need to RW to the same txt file, but they don't have access to the network, so I'm looking for somewhere I can host a txt file, suitable for RW from excel across multiple sites.

I have been looking at FTP, but not sure if I can get Excel to RW directly to a txt file in an FTP location. Would rather not have to build an SQL DB instead of using a simple TXT file, but I'm starting to think that's my only option.

Any suggestions welcome.

I have tried Sharepoint Bernie, but couldn't work out a way to get Excel VBA to append to a txt file on a sharepoint folder. Have you seen this done successfully in the past?
I've just set up a MySQL database on an online server, but am now struggling to make a connection to it via SSH from VBA. I'll post another post about that.