Facebook get page publish token not working

Question

We've been using this link for years to get a token so we can publish on facebook pages on behalf of the user:

https://www.facebook.com/dialog/oauth?response_type=token&scope=pages_manage_posts&client_id=XXXXX&redirect_uri=XXXXX

But now it won't return to our page after selecting the pages to grant access to. All we get is a facebook page saying "This content is not available right now".

It stopped working mid september I think. Did FB change something?