How to add msg payload to outgoing json fields for hangouts

I’m using the google hangouts integration to send notifications to my phone
I’m using node-red for my automations.
If I define a static message in the json of the node red, it will send to hangouts.
but if i want to add something dynamic, like something from another node, how do I add that into the message that is being sent out?

for example, If i wanted to send a message that the temp of the freezer was to high
I can send a static message saying it’s too high. but how do i add the current temp into the message?