I don't know, where to start. I'm integrating PayPal Express Checkout in my RoR application in my Localhost server. 

Yes, I'm using a gem, [merchant-sdk-ruby](https://github.com/paypal/merchant-sdk-ruby). 

In this integration, I'm trying to follow this working flow:
![enter image description here](https://i.stack.imgur.com/FRKpC.gif)

1. set\_express\_checkout
2. get\_express\_checkout
3. do\_express\_checkout

In `set_express_checkout` I'm able to generate `token` successfully and able to redirect to <https://www.sandbox.paypal.com/webscr?cmd=_express-checkout&token=EC-93W211694E768010D> here with my generated token. 

Inside the method which generates `token`, I mean in `set_express_checkout`, I had to provide 3 URL. 

1. **ReturnUrl**
2. NotifyUrl
3. CancelUrl

Isn't it ReturnUrl (a URL of my application **(which in localhost)** with `token` and `payerID`) in which PayPal redirects after generating Checkout Details? 

My Question is:
**Does PayPal redirects in a specific URL of my Application which is hosted on my Local Server?**

Please help to integrate PayPal Express Checkout in my localhost.