Post changing data with the HTTP addon to IFTTT?

I would like to use the HTTP addon to post changing data from several things or variables to IFTTT by using the IFTTT webhook trigger.

I can add a constant query parameter with the HTTP addon and that works perfectly.
For example by such a setting in the HTTP addon:
A list of query parameters
A parameter*
The name of the parameter*
The value of the parameter*

But I have no idea how I can include a changing parameter from a variable like a temperature value. How do I have to do this? Many thanks.