FTP helper problem

If I select any of the Match helper (eg. FTP passive connection tracking) in the port forwarding advanced tab, the port seems to be closed, any connection refused.

This is the correct operation?

To better assist you, please show us the complete firewall rule you created to open the port.

Sorry, here is the section in the /etc/config/firewall:

config redirect
	option dest 'lan'
	option target 'DNAT'
	option name 'Raspi ftp'
	list proto 'tcp'
	option src 'wan'
	option src_dport '7721'
	option dest_ip ''
	option dest_port '21'
	option reflection '0'
	option helper 'ftp'