Meta Slider no “add new” button

Hi –
I just installed the Meta Slider Pro Add on to create a post slider.

Then I tried to follow the documentation, but failed right at the first step:

There is written “Click the ‘Add Slide’ button to launch the Media Manager and select ‘Post Feed’ from the left.”

My problems:
1. I don’t have a button that is named “add slide”
(only a “+” button that doesn’t show the desired view)
2. I can’t find any other buttons or else to launch the media manager

I’ve added a image of my dashboard. Maybe someone can tell me if something is missing, or if I’m simply too stupid.
https://www.bilder-speicher.de/16111915674547/foto/dashboard—meta-slider-options.html
(Hope this works)

Would be thankful for your help
Regards Reca