As PHP 7.4 released recently so there may be chances to face issues with the new versions. So sometimes we need to downgrade PHP from the latest version. Follow the below steps to downgrade PHP to 7.3

sudo add-apt-repository ppa:ondrej/php

sudo apt-get update

sudo apt-get install php7.3

sudo apt-get install php7.3-cli php7.3-common php7.3-json php7.3-opcache php7.3-mysql php7.3-mbstring  php7.3-zip php7.3-fpm php7.3-intl php7.3-simplexml

sudo a2dismod php7.4

sudo a2enmod php7.3

sudo service apache2 restart