Could not get lock /var/lib/dpkg/lock-frontend. It is held by process 6991 (aptd) code example

Example: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), is another process using it?

ps aux | grep -i dpkg

// Kill processes which are running
sudo kill -9 <pid>

// Restart the accounts daemon
sudo systemctl restart accounts-daemon