fixed the ‘You must provide a valid Privacy Policy URL in order to disable Sandbox Mode.’

Recently some of my visitors told me that they couldn’t using the Facebook login action. And then I try to fix this bug. Long time passed, There os no result.Then I went to have a look the settings of my application in the facebook, and I found that the Sandbox Mode is On. When I tried to turn it off, the page told me ‘You must provide a valid Privacy Policy URL in order to disable Sandbox Mode’. OK, let me find where can I setting the Privacy Policy URL, then I find it in the App Details page. After set it, I turn the sandbox mode off.