Before anything, please note that I have found several similar questions on Stack Overflow and articles all over the web, but none of those helped me fix my issue:
Step 1:
cd /etc/postgresql/12/main/
open file named postgresql.conf
sudo nano postgresql.conf
add this line to that file
listen_addresses = '*'
then open file named pg_hba.conf
sudo nano pg_hba.conf
and add this line to that file
host all all 0.0.0.0/0 md5
It allows access to all databases for all users with an encrypted password
restart your server
sudo /etc/init.d/postgresql restart