Highcharts not working
I was thoroughly mistaken about the installation of the charts. After installation, I was editing the repositories section in composer.json  and running the composer command to install the specific library (eg: composer require --prefer-dist highcharts/highcharts:6.0.4) from the particular sub-module. But it has to be done from the Drupal project root directory. Appreciate your valuable time and expecting this will help others.