Accessing localhost from another virtual machine

I have 2 Virtual box vm instances, one is running Ubuntu hosting a web with Django built-in server, listening to port 3000. The other is running Kali Linux. I want to access the web hosted on Ubuntu on Kali Linux, so I typed the private ip on the Kali Linux browser, but it says unable to connect to that IP address.

I read this post Ubuntu's local host can be accessed without firewall setting

How can I achieve that?