OAuth & facebook access_token not working, need OAuth expert

Question

I have read the 1000+ blogs about how the redirect_uri has to be the same in both calls to OAuth in order to get a user token, but 100% of the time, regardless of how I format the URL, it fails with:

{
   "error": {
      "message": "Error validating verification code. Please make sure your redirect_uri is identical to the one you used in the OAuth dialog request",
      "type": "OAuthException",
      "code": 100
   }
}

I have been meticulous in making sure that the URLs in both calls were the exact same. My URL has to have a ? in it and I have tried replacing it with %3f but that didn't help. There has to be something else that can cause this error, I need to learn what that might be?

This seemed to break for me over the past month sometime. We did a show in late July and things worked fine (had a different base URL for that show since it was a different server). Could it be that the URL is of this format:

someprestuff.morestuff.mainurl.com?prm=value

Are there too many "parts" to the URL for Facebook to accept it?

I'm looking for alternate things to look for.

Answer 1

The url should be the same and it has to be escaped. In the url it has to look like this:

http%3A//someprestuff.morestuff.mainurl.com%3Fprm%3Dvalue

Answer 2

Jim's comment above worked, but to clarify, it was a forward slash that fixed it for us.