Well just what i thought pure-ftpd was not fully installed. I also soemthing to indicate it here FTP not working - 530 Login authentication failed - #9 by savors.map when you creating a user for pure-ftpd.
RUn this line by line dont skip
sudo apt-get remove --purge pure-ftpd pure-ftpd-common
sudo apt autoremove
sudo apt install pure-ftpd -y
groupadd -g 2001 ftpgroup
useradd -u 2001 -s /bin/false -d /bin/null -c "pureftpd user" -g ftpgroup ftpuser
systemctl start pure-ftpd
mkdir /etc/ssl/private
openssl req -newkey rsa:1024 -new -nodes -x509 -days 3650 -subj "/C=US/ST=Denial/L=Springfield/O=Dis/CN=www.example.com" -keyout /etc/ssl/private/pure-ftpd.pem -out /etc/ssl/private/pure-ftpd.pem
rm -R /etc/pure-ftpd
mkdir /etc/pure-ftpd
cp /usr/local/CyberCP/install/pure-ftpd-one/* /etc/pure-ftpd/
systemctl restart pure-ftpd