Invoke a html on POST request

What are the approches to load a web application inside another application by sending a POST request.
In my scenario there is an android app which send a POST request and needs to render a html page inside the android app. That html will subsequently perform other actions with a backend.
The implementation of android part is not relevant since it done by another party and the initial request to load the app initially will always be a POST request. No control on that.

What I have to do is, get that POST request and give a html. I would prefer angular.
I know there is no such thing called POST request to load an angular app(or any client application).

I came across angular universal which facilitates server side rendering. But I am having an .net application(web api) as the backend
not a .netcore application. As per my understanding angular universal can be used with .netcore applications.

Another approach is to send the POST request to a traditional mvc controller and return a razor view with proccessed data.
But I prefer to use an angular app without getting razor views involved.

Please give me some ideas on how to approch this kind of scenarion. Thanks.

Source: AngularJS