FTP read only access for single user on SMB share

I have been asked to set up an SMB share to migrate a large amount of image data into (approx 150TB) which will be writable for one AD user (service account). This is not a problem, I have set this up and the user can access fine.

However, I also need to grant access on this share to a single user to be able to read the files using FTP. We have FTP enabled, and I have created a local user account. Local user can access their home drive if I connect through WinSCP or Filezilla on port 21, can navigate to the folder that is shared, but cannot see any files in it. I am struggling with how to grant them the right read only permissions on the folder. I'm also unsure of the purpose of enabling server to server transfer and whether I will need to do this too.

I wondered if anyone could point me in the right direction or indeed if I'm doing something really silly that I shouldn't be doing, please tell me so!