using paid button

src/gui/mainwindow.h

@@ -17,10 +17,12 @@ class MainWindow : public QMainWindow
     MainWindow();
     Marketplace* getMarketplace() { return marketplace_.get(); }
 
-  private:
+  private slots:
     void on_actionEditSeller_triggered();
     void on_sellerNoEdit_checkSellerNo();
+    void on_paidButton_triggered();
 
+  private:
     Ui::MainWindow ui_;
     std::unique_ptr<Marketplace> marketplace_;
 };