Unable to assing Einstein Activity Capture to users

Hello everyone,

I'm facing an issue that I don't find any answers to. I want to set up Einstein Activity Capture Standard. When I try to assign users to the permission set Standard Einstein Activity Capture I get this :  

All Standard Einstein Activity Capture User permission set licenses are in use. For more licenses, contact your salesforce.com representative.

But when I go to company informations I see that the status of Standard Einstein Activity Capture User permission set license is set to "Disabled", 0 licenses, and the expiration date was on 10/01/2021.

Can someone explain to me how this works ? Does add more licenses will have a pricing ? have those permission set licenses always an expiration date ? How to add more of this license ?

Thanks in advance