Multicast Traffic Forwarding over IPSec vpn

We are trying to forward multicast traffic for 239.1.1.2 between our Main Site to one of our remote sites via a Site-to-Site IPSec VPN connection.

I have following the instructions here: https://support.sophos.com/support/s/article/KB-000038580?language=en_US

But when I add the Multicast address to the Site-to-Site VPN configurations of our main site and the remote site, the VPN connection goes down, and they won't establish the connection until I remove the Multicast address from the Site-to-Site configurations...

I'm stumped as to why this is happening.

The instructions say to "add the multicast IP address/network in the Remote subnet section". 

So I created the following and added it to the VPN configurations:

Any ideas of what would cause this?