It can actually be retrieved using the Getvar AMI action[1]. There’s no need to specify a channel. It accepts dialplan functions as well as dialplan variables. So you’d use it like this for example:
Thanks all for your great help!
Since I wasn’t able to fetch the value of the variable via AMi > Getvar… I added a counter when the call arrives at our PBX & added a hangup handler to decrease the count.