So, two separate things here.
You say you have the JSONPATH Transformation Service installed, but the above log entry is saying you don’t. Can you show us that it is installed? Perhaps try uninstalling and reinstalling it.
For what reason? Just for display somewhere?
This tutorial is almost exactly what you’re doing, except I used a Sonoff Basic and added a DHT22 sensor myself. See if it helps with the setup, as it also shows how to add units for display…