使用Android购买状态API：未找到

我有一个android应用程序，它正在使用“谷歌应用内付费”库在应用内购买

我已经读过，最好使用购买状态API（Google Play Android Developer API v1.1）在后端服务器中验证购买

我发现了一个关于如何获取刷新令牌、如何使用它获取访问令牌以及如何使用API的示例

HttpHost proxy = new HttpHost("10.12.54.8", 8080, "http");

HttpClient client = new DefaultHttpClient();
client.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY, proxy);
ApacheHttpTransport HTTP_TRANSPORT = new ApacheHttpTransport(client);

JsonFactory JSON_FACTORY = new JacksonFactory();   

TokenResponse tokenResponse = new TokenResponse();        
tokenResponse.setAccessToken(accessToken);
tokenResponse.setRefreshToken(refreshToken);
tokenResponse.setExpiresInSeconds(3600L);
tokenResponse.setScope("https://www.googleapis.com/auth/androidpublisher/v1.1/applications");
tokenResponse.setTokenType("Bearer");

HttpRequestInitializer credential = new GoogleCredential.Builder().setTransport(HTTP_TRANSPORT).setJsonFactory(JSON_FACTORY)
                .setClientSecrets(GOOGLE_CLIENT_ID, GOOGLE_CLIENT_SECRET).build().setFromTokenResponse(tokenResponse);

AndroidPublisher publisher = new AndroidPublisher.Builder(HTTP_TRANSPORT, JSON_FACTORY, credential).setApplicationName(GOOGLE_PRODUCT_NAME).build(); 

AndroidPublisher.Inapppurchases purchases = publisher.inapppurchases();
Get get = purchases.get(GOOGLE_PACKAGE_NAME, ITEM_ID, purchaseToken);
InappPurchase purch = get.execute();

但我收到一封404找不到的信。为什么?

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提前谢谢。

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