Ubuntu 18.04 ProFTPD module not working


Just installed Virtualmin on Ubuntu 18.04.

The ProFTPD module responds:

The program /usr/sbin/proftpd does not appear to be the ProFTPD server. Maybe it is not installed, or your module configuration is incorrect. Output from the command /usr/sbin/proftpd -v was :

Command netstat -aln | grep :21 output:
tcp6 0 0 :::21 :::* LISTEN

Command which proftpd output:

Command /usr/sbin/proftpd -v output from terminal:
ProFTPD Version 1.3.5e

What’s wrong here?

Thank you very much.