Why is it impossible to send requests to a gray IP normally?

Question

PHP

After all, when a client with a gray IP sends a request, the response is addressed to him, which means that you can somehow address it. So why can't you connect to a gray IP then? I mean not directly (this will obviously be a hemorrhoid for users, since you can’t do without additional software), but using hosting (it has a white IP, a second-level domain, and there are php and mysql tools).

Answer 1

The router remembers for whom it sent the request outside, and therefore always knows to whom to return the answer.
It won't help you.