Unable to connect to an postgresql ec2 instance from pgadmin4

I created an EC2 instance and then installed postgresql (version 11) and timescaledb in it. My security group looks as follows:

As of now, I have enabled this instance for all the IP addresses.

My /etc/postgresql/11/main/pg_hba.conf looks like this:

# Database administrative login by Unix domain socket
local   all             postgres                                peer

# TYPE  DATABASE        USER            ADDRESS                 METHOD

# "local" is for Unix domain socket connections only
local   all             all                                     peer
# IPv4 local connections:
host    all             all             127.0.0.1/32            md5
# IPv6 local connections:
host    all             all             ::1/128                 md5
# Allow replication connections from localhost, by a user with the
# replication privilege.
local   replication     all                                     peer
host    replication     all             127.0.0.1/32            md5
host    replication     all             ::1/128                 md5
host    all             all             0.0.0.0/0               md5 #ipv4 range
host    all             all             ::0/0                   md5 #ipv6 range
host    all             all             all                     md5 #all ip

and the /etc/postgresql/11/main/postgresql.conf looks like this:

# - Connection Settings -

listen_addresses = '*'          # what IP address(es) to listen on;
                                        # comma-separated list of addresses;
                                        # defaults to 'localhost'; use '*' for all
                                        # (change requires restart)
port = 5432                             # (change requires restart)
max_connections = 100                   # (change requires restart)

Then, I try to connect to the database via Pgadmin4 using the Public DNS(IPv4):ec2-xx-xxx-xxx-xxx.eu-central-1.compute.amazonaws.com

After I enter the username and password, it throws the following error:

Unable to connect to server:

could not connect to server: Connection refused
Is the server running on host "ec2-xx-xxx-xxx-xxx.eu-central-1.compute.amazonaws.com" (xx.xxx.xxx.xxx) and accepting
TCP/IP connections on port 5432?

I had a look at the following post and followed all the instructions, but to no avail:

1. connect-to-remote-postgresql-server-on-amazon-ec2

Can anyone please help me out with this?

Edit 1

When I do:

/etc/init.d/postgresql restart

I get:

[....] Restarting postgresql (via systemctl): postgresql.service==== AUTHENTICATING FOR org.freedesktop.systemd1.manage-units ===
Authentication is required to restart 'postgresql.service'.
Authenticating as: Ubuntu (ubuntu)
Password: 

I don't know what password to enter here so that the postgresql can get restarted