Connecting from iOS to macOS using ssh
Using the GUI

This is the easier way to do it:

Go to System Preferences.app then go to "Sharing" and then enable "Remote Login" 

Using the Command Line:

If you insist on using the command line, I think the command you're looking for is:

sudo launchctl start com.openssh.sshd

I think the syntax may vary somewhat if you are using an older version of macOS you are running, but I don't remember when that might have changed, so I can't say for sure.