Problem to parse an json mqtt message

I have many working sensors connected over MQTT. My new sensor is sending an JSON string instead of a value.
When I look in my broker the message looks like this:

I’m trying to get this into an number item in OH, but without any success. I guess it should be something like this…
Number Temperature_Pool … { mqtt="<[broker:tele/pool/SENSOR:state:“some magic transform”]" }

I hope that there are somewhere out there that knows how to “transform this” = get only the temprature reading, or point me to somewhere where I can learn more about regex / JSON transformations.

I have also tried using JSONPATH like this
{ mqtt="<[broker:tele/pool/SENSOR:state:JSONPATH($.DS18B20[Temperature])]" }
But that also fails…

For the record if anyone else is having the same problem…

By altering the syntax in the JSONPATH to ($DS18B20.Temperature) it works fine!