How to post value to multi php page?

Question

the input button is in index.php

Answer 1

You cannot use standard HTML forms to send requests to three different pages in this way. A form is designed to send an HTTP request to only one location.

Ideally, you would have a single target.php file which then calls files 1.php 2.php and 3.php on the server through include, merges the results, and sends them back to the user.

Failing that (for instance, some of the files are on different servers), you could use redirection: 1.php redirects to 2.php when it's done, and so on.