Can't give an AJAX request?

Question

AJAX

I wanted to give a request for one API with Basic Auth (USERNAME - PASSWORD).
Created index.php - added header header('Access-Control-Allow-Origin: *');
Wrote script - send AJAX on button click

function myFunction(){
        var username="xxx";
        var password="xxx";
        $.ajax({
          type: "GET",
          url: "xxx",
          dataType: 'json',
          headers: {
            "Authorization": "Basic " + btoa(username + ":" + password)
          },
          success: function (result){
              console.log(result)
          }
        });

In response I receive

Access to XMLHttpRequest at 'xxx' from origin 'https://Мой серв.kz' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

Tried a lot of things but it doesn't help.

Answer 1

https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS