Hi Derx! Dan from MindMeister here. Regarding the ID, this refers to the unique numeric code associated with a public map. I.e.
https://www.mindmeister.com/40950677/how-to-win-friends-influence-people
would have the ID of 40950677
To use the plugin, you can enter one of two lines of code:
[mindmeister id="40950677"]
or
[mindmeister url="https://www.mindmeister.com/40950677/how-to-win-friends-influence-people"]
Regarding the slug, I believe OncleTom is trying to pull information from a Private Map, which after my own testing will not display, even when logged into MindMeister. For information on making maps public, please see here:
https://www.mindmeister.com/blog/2010/11/05/access-denied-%E2%80%93-or-how-to-share-your-mind-maps/
