Load custom external page on wordpress + dynamic url

This might be a tricky one but let’s try.

I’m hosting a wordpress website on domain.com.
This website has several pages such as

domain.com/about
domain.com/product

Now, im having another product which is made as vue website which is hosted on app.domain.com

This vue application is offering option for users to create their own urls such as:

app.domain.com/bill
app.domain.com/michael

on top of that each user can create their own subpages so for example bill user he could create:

app.domain.com/bill/30-minutes
app.domain.com/bill/60-minutes

So, what I would like to do is somehow in my WordPress site to load these external pages so they become like.

domain.com/bill
domain.com/bill/30-minutes

I don’t want to have a redirect, but I want to keep the URL.
So What I can do is some sort of coding to fetch these landing pages,

But my question is how do I rewrite this for WordPress or NGINX that I’m running?
So for example:

domain.com/bill that I should make a request to another page, and not try to load a wordpress page.

Any suggestions are welcome

Thanks in advance.