user is not in the sudoers file

sudo vim /etc/sudoers

#

# This file MUST be edited with the 'visudo' command as root.

#

# Please consider adding local content in /etc/sudoers.d/ instead of

# directly modifying this file.

#

# See the man page for details on how to write a sudoers file.

#

Defaults    env_reset

Defaults    mail_badpass

Defaults    secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin"

# Host alias specification

# User alias specification

# Cmnd alias specification

# User privilege specification

root    ALL=(ALL:ALL) ALL

# Members of the admin group may gain root privileges

you sould add your user below the "root ALL=(ALL:ALL) ALL" like this:

# User privilege specification

root    ALL=(ALL:ALL) ALL

user    ALL=(ALL:ALL) ALL