Here you have a description of the API:
[url=https://www.domoticz.com/wiki/Domoticz_API/JSON_URL's] Domoticz API[/url] .
For what you want, you need to create a virtual sensor (dummy).
You need to know its IDX. Scroll down to the "Temperature" section in the link what I gave you and you will see the syntax of the link:
/json.htm?type=command¶m=udevice&idx=IDX&nvalue=0&svalue=TEMP
.
You substitute the IDX parameter of your dummy sensor under IDX and your value under TEMP.
