Hi,
I have activated Picklist plugin, and my custom plugin.
In the plugin functions.php, I have added the code here to build a simple Admin Page, but the menu item is not displayed.
Before, I have tried some code in meta-boxes, but the meta box created didn’t appear when I created a new post.
I have attached some screens to let you see.
Edit:
I add the plugin main code here :
https://www.dropbox.com/s/zc04o46csiss9yw/Capture%20d%E2%80%99%C3%A9cran%202018-05-17%20%C3%A0%2011.50.56.png?dl=0

Thanks for your help!
Alex