我有以下问题，我在我的移动应用程序购买。当用户想要购买时，单击“购买”按钮后，会出现一个带有价格的窗口。用户购买后，“购买”按钮将隐藏，并显示“下一步”按钮。问题是，当用户想再次查看内容并单击“购买”时，会出现一条消息
“您已经购买了此产品”，下一步按钮仍然隐藏。
以前，一切正常，一次性付款后，用户随时可以查看内容，代码如下：

BillingProcessor bp;
Button buy, next;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_my_class);

    bp = new  BillingProcessor(this,"",this);
    buy = (Button)findViewById(R.id.buy);

    next = (Button)findViewById(R.id.next);

    next.setVisibility(View.INVISIBLE);

    buy.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            bp.purchase(MyClass.this,"android.test.purchased");

        }
    });

    next.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            Intent intent = new Intent(view.getContext(),NewClass.class);
            startActivityForResult(intent,0);

        }
    });

}

@Override
public void onProductPurchased(@NonNull String productId,@Nullable TransactionDetails details) {

    buy.setVisibility(View.INVISIBLE);
    next.setVisibility(View.VISIBLE);

}

@Override
public void onPurchaseHistoryRestored() {

}

@Override
public void onBillingError(int errorCode,@Nullable Throwable error) {

}

@Override
public void onBillingInitialized() {

}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (!bp.handleActivityResult(requestCode, resultCode, data)) {
        super.onActivityResult(requestCode, resultCode, data);
    }
}

@Override
public void onDestroy() {
    if (bp != null) {
        bp.release();
    }
    super.onDestroy();
}