Hello all.
Just installed a fresh copy of ubuntu 20.04 on a VPS on Oracle Cloud. Installed the aaPanel using the installation command wget -O install.sh http://www.aapanel.com/script/install-ubuntu_6.0_en.sh && sudo bash install.sh aapanel
Installation completed with the following output:

==================================================================
Congratulations! Installed successfully!
==================================================================
aaPanel Internet Address: http://<PUBLIC_IP>:8888/c37a3a44
aaPanel Internal Address: http://10.0.0.213:8888/c37a3a44
username: dnxja8lh
password: 2835951d
Warning:
If you cannot access the panel, 
release the following port (8888|888|80|443|20|21) in the security group
==================================================================

I have intentionally hidden the Public IP.

Problem

Can't access the aaPanel on port 8888.
Can't access the website either on port 80 nor on port 443

What I did.

Made sure that the ports are open on the VPS Firewall. (Just to be sure I wasn't making any mistake, I opened up all the ports) - Still not accessable.
Connected to the VPS using SSH. And tunneled port 80 and 8888. Now it did work. I was able to access the aaPanel dashboard and install Nginx stack.
Deleted and added firewall entries to allow port 80, 443, 8888, 888. Still not accessible over public IP.
Installed Docker from the aaPanel itself and installed Portainer. Portainer has a web UI at port 9000. I tried to access this UI and again. IT WORKS.

At this time I am sure that it something to do with aaPanel itself. Or is it me doing something wrong? I even disabled the ubuntu firewall using the command sudo ufw disable.

Output of sudo lsof -i:80

COMMAND  PID        USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
nginx   1109        root    9u  IPv4  20409      0t0  TCP *:http (LISTEN)
nginx   1111         www    9u  IPv4  20409      0t0  TCP *:http (LISTEN)
nginx   1112         www    9u  IPv4  20409      0t0  TCP *:http (LISTEN)
nginx   1113         www    9u  IPv4  20409      0t0  TCP *:http (LISTEN)
nginx   1114         www    9u  IPv4  20409      0t0  TCP *:http (LISTEN)

Looks like Nginx is working fine.
CURLed localhost on port 80

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Site not found</title>
<style>
*{margin:0;padding:0;color:#444}
body{font-size:14px;font-family:"宋体"}
.main{width:600px;margin:10% auto;}
.title{background: #20a53a;color: #fff;font-size: 16px;height: 40px;line-height: 40px;padding-left: 20px;}
.content{background-color:#f3f7f9; height:300px;border:1px dashed #c6d9b6;padding:20px}
.t1{border-bottom: 1px dashed #c6d9b6;color: #ff4000;font-weight: bold; margin: 0 0 20px; padding-bottom: 18px;}
.t2{margin-bottom:8px; font-weight:bold}
ol{margin:0 0 20px 22px;padding:0;}
ol li{line-height:30px}
</style>
</head>

<body>
        <div class="main">
                <div class="title">Site not found</div>
                <div class="content">
                        <p class="t1">Your request did not find this site in the web server!</p>
                        <p class="t2">Probable cause: </p>
                        <ol>
                                <li>Did not bind this domain name or IP to this site!</li>
                                <li>Configuration file not in effect!</li>
                        </ol>
                        <p class="t2">How to solve: </p>
                        <ol>
                                <li>Check whether already bound to the site, if true, try reloading the Web services.</li>
                                <li>Check if the port is correct.</li>
                                <li>If you are using a CDN product, try clearing the CDN cache.</li>
                                <li>For ordinary website visitors, please contact the webadmin.</li>
                        </ol>
                </div>
        </div>
</body>
</html>

CURLed on localIP (10.0.0.213), STILL WORKS

CURLed public IP:

curl: (7) Failed to connect to 152.xxx.xxx.xxx port 80: No route to host

CURLed <PUBLIC_IP>:8888

curl: (7) Failed to connect to 152.xxx.xxx.xxx port 8888: No route to host

CURLed 10.0.0.213:8888

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<title>Redirecting...</title>
<h1>Redirecting...</h1>
<p>You should be redirected automatically to target URL: <a href="/login">/login</a>.  If not click the link.

So, I tried my best. I don't know what's wrong.

Looking for a solution. Thanks in advance.