Not able to access REST APIs hosted on ubuntu VM from windows browsers

I'm working on windows 10 and installed ubuntu virtual machine on it. In ubuntu VM, Laravel REST API service is running on port 80. When my front-end application (on windows browser) tries to call/access these REST APIs, the application is getting "503 Service Unavailable" as response. But if I try to ping to this server, it is sending and receiving some bytes of data. Only curl call and windows browsers are not able to access these REST APIs.

However, In another ubuntu VM (say vm2), if I try to fetch resource from these REST APIs, sometimes it works and sometimes it gets the response same as that of windows browser (503). This is a weird behavior on vm2, since it cannot be predicted when the API call succeeds and when not.

I have checked hosts file in windows, port-forwarding in virtual box, apache2 configurations and other related files.

But nothing worked so far. Any help would be appreciated. Thank you.