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.
In this integration, I'm trying to follow this working flow:

- set_express_checkout
- get_express_checkout
- 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.
- ReturnUrl
- NotifyUrl
- 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.