Yeah, the firmware that enables Sense (MV 3.22) is still in Beta.
@Toogii, you could upgrade your cameras' firmware to MV3.22 and go to the Settings page of each camera to enable Sense and set it up with your MQTT broker, or use the REST API.
Everyone with an MV network on their organization got 10 MV Sense licenses for free, so you can try it out without buying any other license for now. Each camera you enable Sense on counts towards those 10 licenses, which means you can use the people-counting API on 10 of your cameras for free.
Take a look at this page as well, it walks you through the setup process, as well as the API calls:
https://documentation.meraki.com/MV/Other_Topics/MV_Sense