www/api/delete_device.php

<?php
declare(strict_types=1);
require __DIR__ . '/db.php';

$data = json_decode(file_get_contents("php://input"), true);
if (!$data || !isset($data['uid'])) {
    http_response_code(400);
    echo json_encode(["error"=>"invalid"]);
    exit;
}

$uid = $data['uid'];

$pdo->prepare("DELETE FROM contadores WHERE uid=?")->execute([$uid]);

echo json_encode(["ok"=>1]);