How to post a post to facebook group via api?

Question

Python

I did this, but it doesn't work for me:

https://graph.facebook.com/v2.12/group_id/feed?post&message=Testing&access_token=token

Although if I do myself on the wall, then everything is fine.

https://graph.facebook.com/v2.12/me/feed?post&message=Testing&access_token=token

ps I'm an admin in the group
ps I still need to add a photo, if you add "&picture=url" (url - link to the photo), then it says - "(#100) A link must be provided if a picture URL is given."