The Built in Rest service call won't work, because first you have to answer to a HTTP POST request and get that raw data processed!!!!!
Hey Andy,
You have writen that you are using the REST service module. However with Mendix 6.8.0 it is recommended to use the Mendix built in Rest service call. This is one of the selectable blue blocks. Documentation can be found from within the modeler regarding the mapping and making of JSON structures. To get you started you could look here.
If you do want to use the old version you only need to use a java action and an object in the same form as your Jason as explained here
I have a loranode that spits out data to a URL I can specify (i.o. my mendix project). I will explain later.