Graph error when trying to activate plugin on facebook

Hi,

I installed the plugin on multiple pages, so far no problems. On the latest page that I’m working to setup instant articles, this error appears after I select the FB page to publish:

ERROR – Graph returned an error: Error validating verification code. Please make sure your redirect_uri is identical to the one you used in the OAuth dialog request

This usually only happens when there is a / or something like that missing in the redirect url. But I don’t get how the redirect url can be wrong or different, it doesn’t make too much sense. Any ideas how to solve this?

https://ww.wp.xz.cn/plugins/fb-instant-articles/