Facebook redirect url issue OAuthException

Question

My app was working well for long time, but now I am getting the error from Facebook saying:

Content: {\"error\":{\"message\":\"Error validating verification c

Answer 1

in my case it caused by special characters in my query string, i had base64 code that contain / and =, i tried some characters like ! @ = / ; all throw same error

only two character that look like is valid is - _ # $

P.S / at the end of the query didn't help. also it was forbidden in the middle of the query string