we are currently running 9406 on a windows machine. We've built a mailing list system into our CMS using the standard SM API's for mailing list and everything works great on that front. However, we are now trying to deal with unsubscribes. 
In our mailouts we have a link to unsubscribe, which works as expected, but if someone clicks the unsubscribe option in the header of the email, it sends the standard unsubscribe to the SM server instead of directly to our web server to process. We are hoping to get around this using the Webhook option for "Mailing List Unsubscribe", but ran into a snag. In the webhook action, we set the URL (this calls correctly) and we are setting payload (this is also getting sent) however, when we try to use variables in the "webhook payload" section, SM isn't replacing the variables. For instance, in order for our CMS to properly remove someone from our systems, we need the #toaddress# and the #listname# (ideally i'd like more like the list address ID, but i can work this with). 

Someone at some point mentioned that only the "webhook url" would properly replace the variables, and if so i would think this is a slight oversight? We've tried everything we can think of based on the documentation. here is the payload we are trying to send for reference, just in case our code is the problem?

{"toaddress":"#toaddress#","listname":"#listname#"}