From Electron's `main.ts`:
```
import { BrowserWindow, ipcMain } from 'electron';
...typescript
ipcMain.on(
    'close-paypal',
    () => {
        BrowserWindow.getAllWindows().forEach((win) => {
            // The Paypal window would fail to load contents due to security 
            // restrictions and return an empty URL
            if (!win.webContents.getURL()) {
                win.close();
            }
        });
    }
);
```

From your content script (I'm using TypeScript):
```typescript
const { ipcRenderer } = require('electron');
...
paypal.Button.render({
  ...
  payment: () => {
      ipcRenderer.send('close-paypal', '');
      // Other logic to trigger payment flow
  }
  ...
});
```