Can't Access Instance Through Web Browser (READ EDIT)

My YunoHost server

Hardware: Virtual Machine
YunoHost version: 11.0.9
I have access to my server : Through the webadmin
Are you in a special context or did you perform some particular tweaking on your YunoHost instance ? : No

Description of my issue

So, I installed YunoHost through VirtualBox as I had no USB flash drive to create a server for the long run. I was able to enable port forwarding on my WiFi router, and I have everything working through my end. The only problem I have is that I can’t access my instance through my own browser, not even on other devices that I have.
I am not sure if it is because I used VirtualBox as a means to create the server.
Would I have to create a long-term server for this? Please give me any tips to solve this! I am still new to self-hosting! Thank you!

EDIT: So I created the Let’s Encrypt certificate and now I can see the website! Only problem is that when I logged in with my credentials, I saw a screen for nginx that says:

Welcome to nginx! If you see this page, the nginx web server is successfully installed and working. Further configuration is required. For online documentation and support please refer to nginx.org.
Commercial support is available at nginx.com. Thank you for using nginx.

What kind of configuration should I do to get the website running?

For some reason, even though I enabled port forwarding, the ports cannot be accessed through IPv6.