how to insert a mysql record into array [ONESIGNAL script]?

Question

how can i get userid from my mysql database and implement it in the code. I can't use regular PHP variable.

$device_id = mysqli_query($conn,"SELECT notification_id FROM app WHERE customer_id='$form_customer_id' AND status='ACTIVE'");
if(mysqli_num_rows($device_id) >= 1) 
{ 
while($row = mysqli_fetch_array($device_id))
{
$onesignal_id=$row['notification_id'];
}}

and here is a code

    $content      = array(
        "en" => 'TEST PUSH MES'
    );
    $hashes_array = array();
    array_push($hashes_array, array(
        "id" => "like-button",
        "text" => "Like",
        "icon" => "xxx",
        "url" => "xxx"
    ));
    array_push($hashes_array, array(
        "id" => "like-button-2",
        "text" => "xxx",
        "icon" => "xxx",
        "url" => "xxx"
    ));
    $fields = array(
        'app_id' => "xxx",
        'include_player_ids' => array(
        'HERE I HAVE PROBLEM. I need to get the user id at this point from my MYSQL DATABASE'
),
        'data' => array(
            "foo" => "bar"
        ),
        'contents' => $content,
        'web_buttons' => $hashes_array
    );
    
    $fields = json_encode($fields);
    print("\nJSON sent:\n");
    print($fields);
    
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, "https://onesignal.com/api/v1/notifications");
    curl_setopt($ch, CURLOPT_HTTPHEADER, array(
        'Content-Type: application/json; charset=utf-8',
        'Authorization: Basic xxxxxxx'
    ));
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
    curl_setopt($ch, CURLOPT_HEADER, FALSE);
    curl_setopt($ch, CURLOPT_POST, TRUE);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $fields);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
    
    $response = curl_exec($ch);
    curl_close($ch);
    
    return $response;
}

$response = sendMessage();
$return["allresponses"] = $response;
$return = json_encode($return);

$data = json_decode($response, true);
print_r($data);
$id = $data['id'];
print_r($id);

print("\n\nJSON received:\n");
print($return);
print("\n");

I need to get the user ID from the database and put it in the script. Unfortunately, I am learning and I don't really know how to interfere with the code. I thought I could put a variable there, unfortunately it doesn't work

Thx for help! :)