Setup vsftp on Linksys wrt3200acm

please provide a procedure to setup permission vsftp using my Linksys wrt3200acm. My last replacement has problem, keeps going to "permission denied" error. Login (sftpd) used to work on the old router. Do I install vsftpd or vsftpd-tls? I can successfully install vsftpd and add a user but permission is a problem.

That's probably related to dir permissions on OS level.

I can access files from a Win10 PC, same username and passwd but I try using sftp from my Iphone or Ipad, the pop-up for username and password pops up but fails each try. I also want to access the files from the WAN side, (like my old setup).

For debugging purposes, it's usually best to get the phone (and other ftp clients trying to be 'smart' and 'userfriendly') out of the picture. Try to access vsftpd with a cli based ftp client, which doesn't do credentials caching or anything else, check what happens with ls/ dir, cd and (m)put/ m(get) - once you have that working to your expectation, you can rope the smartphone back in.

What I need are instruction to setup a per access login and passwd. The instructions to setup a user is not straight forward and clear.

I believe I have a file permission issue when accessing from vsftpd. Problem is I can't identify the username file permission (ls -l command) after I login using ssh "root" username. I tried chown commands on the files but viewing the none-root permission is not possible. SSH is not setup for login using a username at this time.