Used to use this controller before its update by inputting a targetValue into the controller thus allowing me to use Alexa to change heating thermostat, since the update it wants me to use this json but it fails with an error message of invalid topic?
I would expect the node to want a JavaScript object, not a JSON string. Feed the message into a debug node and show us what you get in the debug pane. You can paste a screenshot here.
I don't know the node you are using, but I would have expected it to want msg.topic and msg.payload. You are setting up msg.payload.topic and msg.payload.payload.
great thanks @Steve-Mcl that fired correctly but is not changing userTargetValue to 25.5 but i can work on that. thanks for the help . this forum never fails to be helpful to us newbies