Trying to connect IBM iSeries (AS/400) to SolarWinds Serv-U FTP

I'm spinning my wheels trying to connect our IBM iSeries FTP to our SolarWinds Serv-U FTP.
I can not establish a connection.  I've tried various options, including port 22, but I always get:

                                                       File Transfer Protocol             


Previous FTP subcommands and messages:                                                   

   Connecting to host ACMEFTP.ACMETOOLS.COM at address using port 21.        

   Cannot connect to host ACMEFTP.ACMETOOLS.COM at address Try again later.

Once I can manually connect, up/download, I will automate it with a script.

I can connect from FileZilla to SolarWinds Serv-U FTP OK, but I need to do it from our iSeries

Suggestions please.  Thank you!