First, you should check whether the client system is properly connected to the internet. If the internet connection isn’t the issue, other common causes for this error include an inactive database or misconfigured file permission.

       
1. Check PostgreSQL status and ensure it is loaded and active. Otherwise, restart it using the following command:
       

sudo systemctl restart postgresql

       
2. If that doesn’t work, check whether the PostgreSQL directory and files permissions are set to 0700 and 0600. To do so, use the following command:
       

ls /var/lib/postgresql/main

       

Then, use the chmod command to change their permissions.