How to add a standalone web application to an existing site?

Question

CMS

There is a working site (apparently on Bitrix) located on the simplest virtual hosting. The task is to create a separate small web application in PHP (for internal use in the company), which, for simplicity, will be available from the same domain, but, importantly, will not affect the already working site in any way.
On the hosting in the file manager there is a public_html folder - as I understand it, these are the site files. I created a separate folder there (conditionally webapp) and added a couple of test files (for example, test.txt). The test file is supposed to be available at site.com/webapp/test.txt, but nothing loads - just a white screen, no error messages.
Perhaps some additional settings need to be changed?

PS And in general, how reasonable is this approach, when we add a separate application to an existing site in this way? Is this a common practice or is it better to make a separate domain for a web application?

Answer 1

1) Set up routing via .htaccess
2) Hang the application on some specific port, for example 8080