Instagram does not redirect the user to redirect-url after login

I have an issue while authenticating Instagram via my application. If the user has not signed in while doing authentication it directs me to Instagram login page after logging in it does not redirect to the app even I have given RedirectUrl in my app and it loads the Instagram page. Moreover, if the user has already logged in and doing authentication means it redirects to my app and works fine. I have tested this case before and it was working fine but now it is not working. Can anyone help me to resolve this issue?