To enable FTPS you need to:
echo 2 > /etc/pure-ftpd/conf/TLS
• 0 disables TLS.
• 1 makes TLS optional for users.
• 2 forces all users to use TLS.
Have the contents of ssl.key + ssl.crt to that it is in:
/etc/ssl/private/pure-ftpd.pem
Afterwards service pure-ftpd restart.