Help! How to POST or use Webhook

I am having some trouble putting in a variable from the core. In the webIDE I used Spark.publish("hana_") and it successfully called the webhook. Now I would like to include data in the Spark.publish function. I looked at some other posts and the data is sent as a string. Example is from another post:

I am assuming the sprintf is creating a string called publishString with the hour, min, sec variables replacing the 3 %u's. The string is then sent to the "Uptime" webhook. I do not understand what the JSON file looks like to receive the string with 3 variables. In the JSON file you shared with me, the values were hard coded. If i wanted to send the temperature value of 75 from the core, I assume the IDE code would be as follows:

Spark.publish("hana_", "{"Temperature":75}";

What would the JSON file look like for receiving the temperature value with the webhook call? Currently the JSON file has a numeric value and not a placeholder for a variable. i.e. "Temperature": "80.2"

Thank you,