[Plugin: Recent Facebook Posts] Display post of closed group

I am trying to display the last post of a closed group page on my website, but I can’t get it work.

Step1 – Getting the facebook id:
With findmyfacebookid I get this error message:
Unable to lookup Facebook numeric ID. Please try again, double-checking the URL of your personal Facebook profile page.

Step2 – Setting the plugin options:
I tried to copy paste the URL of the closed group page in the plugin Facebook Page ID or Slug option (I know I was supposed to provide the facebook id, but since this step failed I wanted to try the URL directly). I got this error:

Facebook error: (#100) Tried accessing nonexisting field (name) on node type (OpenGraphObject)

Question 1:
Is it actually possible to display the last post of a closed group page on a website with the Recent Facebook Posts plugin / the facebook API ?
(seems like it isn’t)

Question 2:
If it’s not possible, would it possible to do it the other way around, i.e displaying the last post of my website on the page of the facebook closed group ?

Thanks in advance for your help,

Julien