Where Do I Find the UPS Call Back URL?

I am trying to set up some shipping methods using the new Oauth version of UPS shipping that was introduced last November or so. However, when setting this up inside my UPS account, they are asking for a callback URL. This is their wording:
External site to which a consumer of this app is redirected to log in when using three-legged OAuth.
Can anyone help me with this? What URL should I enter? Does it matter?

I think I saw on another post that you can leave it empty or enter the url of your wesbite

Please check my answer here:

OK so for the callback URL I just entered the web address of my site.
On the “Test Rate Calculation Tab” I’m getting the following error:
Error Invalid Authentication Information. (Error code: 250002)
Anyone know what could be wrong?

OK I got rid of the error. In the UPS account you have to add the “product” called “Rating” to your app.

But even though that error is now gone and I can get test rates to work in the backend, UPS Ground is not showing up as a shipping option in the front end of the store. Anyone any clues here?

Please contact us via Help Desk for examination.

Not really interested in paying for “fixing” something that should just work.
Are other users able to get this working? I’d like to hear from other users of CS-Cart.