1. 查询已购买商品时没有验证签名 在使用BillingClient查询已购买商品时，需要在查询结果中验证签名以确保商品是经过Google Play Store授权购买的。以下是一个示例：

Kotlin:

fun handlePurchase(purchase: Purchase) {
    if (Security.verifyPurchase(purchase.originalJson, purchase.signature)) {
        // Purchase is verified
    } else {
        // Purchase is not verified
    }
}

Java:

void handlePurchase(Purchase purchase) {
    if (Security.verifyPurchase(purchase.getOriginalJson(), purchase.getSignature())) {
        // Purchase is verified
    } else {
        // Purchase is not verified
    }
}

2. 订阅商品退订时没有向服务器发送请求 当用户通过Google Play Store取消订阅后，应用应该像服务器发送请求以通知用户取消订阅。以下是一个示例：

Kotlin:

fun handleSubscriptionCancel(purchaseToken: String) {
    val params = JSONObject()
        params.put("cancel_subscription", true)
    val requestBody = RequestBody.create(MediaType.parse("application/json"), params.toString())
    val client = OkHttpClient()
    val request = Request.Builder()
        .url("https://example.com/subscriptions/cancel")
        .post(requestBody)
        .build()
    client.newCall(request).enqueue(object : Callback {
        override fun onFailure(call: Call, e: IOException) {
            // Handle network error
        }

        override fun onResponse(call: Call, response: Response) {
            // Handle server response
        }
    })
}

Java:

void handleSubscriptionCancel(String purchaseToken) {
    JSONObject params = new JSONObject();
        params.put("cancel_subscription", true);
    RequestBody requestBody = RequestBody.create(MediaType.parse("application/json"), params.toString());
    OkHttpClient client = new OkHttpClient();
    Request request = new Request.Builder()
        .url("https://example.com/subscriptions/cancel")
        .post(requestBody)
        .build();
    client.newCall(request).enqueue(new Callback() {
        @Override
        public void onFailure(Call call, IOException e) {
            // Handle network error
        }