Php Curl already set authorization but wont work?

I am on a work project using Codeigniter 3. I am trying to hit php restful api with basic authentication using this code generated from postman(already tested in postman and it works) :

<?php

use chriskacerguis\RestServer\RestController;

require APPPATH . 'libraries/RestController.php';


class Api_S extends RestController
{
    public function index()
    {
        parent::__construct();
    }

    public function get_dp()
    {
        $curl = curl_init();
        $username = "xxx";
        $password = "xxx";
        curl_setopt_array($curl, array(
            CURLOPT_URL => 'https://xxx',
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_ENCODING => '',
            CURLOPT_MAXREDIRS => 10,
            CURLOPT_TIMEOUT => 0,
            CURLOPT_FOLLOWLOCATION => true,
            CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
            CURLOPT_CUSTOMREQUEST => 'POST',
            CURLOPT_POSTFIELDS => 'start=2&limit=10',
            CURLOPT_USERPWD => $username . ":" . $password,
            CURLOPT_HTTPAUTH => CURLAUTH_BASIC,
            CURLOPT_HEADER => true,
            CURLOPT_HTTPHEADER => array(
                'api_auth_key: xxx',
                'Authorization: Basic xxx',
                'Content-Type: application/x-www-form-urlencoded'
            ),
        ));

        $response = curl_exec($curl);

        curl_close($curl);
        echo $response;
    }
}

But whenever i try to redirect to call the function get_dp() in Api_S controller the browser shows which ask username and password, but i already defined the username, password and the token in php curl code above. Even when i input it in the alert input field and clicked sign in it wont do anything. What i expect is when i redirect to call the function in api controller it will simply run the function (it will echo the api response) without asking for authorization again since i already include it in the php curl code above. What did i do wrong?How do i achieve that?

UPDATE 1 I also tried to change the code without specifying the authorization information in CURLOPT_USERPWD since its already stated in the request header (CURLOPT_HTTPHEADER) with base64 encoding like below:

<?php
    
    use chriskacerguis\RestServer\RestController;
    
    require APPPATH . 'libraries/RestController.php';
    
    
    class Api_S extends RestController
    {
        public function index()
        {
            parent::__construct();
        }
    
        public function get_dp()
        {
            $curl = curl_init();
        curl_setopt_array($curl, array(
            CURLOPT_URL => 'https://xxx',
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_ENCODING => '',
            CURLOPT_MAXREDIRS => 10,
            CURLOPT_TIMEOUT => 0,
            CURLOPT_FOLLOWLOCATION => true,
            CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
            CURLOPT_CUSTOMREQUEST => 'POST',
            CURLOPT_POSTFIELDS => 'start=2&limit=10',
            CURLOPT_HEADER => true,
            CURLOPT_HTTPHEADER => array(
                'api_auth_key: xxx',
                'Authorization: Basic xxx',
                'Content-Type: application/x-www-form-urlencoded'
            ),
        ));
    
            $response = curl_exec($curl);
    
            curl_close($curl);
            echo $response;
        }
    }

But the above code returns the same result as the previous code. I also tried using similar code as the answer in this link by using curl_setopt($ch, CURLOPT_USERPWD, $username . ":" . $password); and adjust it to my needs like below:

<?php
        
        use chriskacerguis\RestServer\RestController;
        
        require APPPATH . 'libraries/RestController.php';
        
        
        class Api_S extends RestController
        {
            public function index()
            {
                parent::__construct();
            }
        
            public function get_dp()
            {
                $username = "xxx";
                $password = "xxx";
                $ch = curl_init('https://xxx');
                curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/x-www-form-urlencoded'));
                curl_setopt($ch, CURLOPT_HEADER, 1);
                curl_setopt($ch, CURLOPT_USERPWD, $username . ":" . $password);
                curl_setopt($ch, CURLOPT_TIMEOUT, 30);
                curl_setopt($ch, CURLOPT_POST, 1);
                curl_setopt($ch, CURLOPT_POSTFIELDS, 'start=2&limit=10');
                curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
                $return = curl_exec($ch);
                curl_close($ch);
            }
        }

and it still shows the same result.