Created question in FIWARE Q/A platform on 29-05-2019 at 21:05
Please, ANSWER this question AT https://stackoverflow.com/questions/56367445/whats-the-right-way-to-create-a-mosquitto-subscription-with-a-device-and-iotage

Question:
What's the right way to create a mosquitto subscription with a device and IoTAgent-UL

Description:
I'm currently developing a Fiware based network, in which I have devices that report via HTTP and JSON over MQTT and work fine. The network has increased and now I need to attach some devices that use the UltraLight protocol. Doing so, I encountered some troubles.

I followed (to the best of my knowledge) the official documentation provided by the FIWARE Foundation in different sites (the official github repo, readthedocs, and so on). I tried installing the new agent on the same machine as the JSON agent, and it didn't work more on that later. In order to discard any conflicts, I used another VM in which over Docker this time I deployed a new instance of Orion CB, Mosquitto CB, mongo and the agent; a new complete stack of Fiware, basically.

After everything was deployed, I created a new service group on the agent via the rest API (POST /iot/devices), gave it an api key and the CB address. In this step I left the resource field empty, because I don´t really know what role does it play in the whole system. The response was 201, as expected.
The next step was to provision a device, which I did by POSTing to agent/iot/devices with the attributes I wanted, and the api key mentioned in last paragraph. Once again, the response was 201.

The problem arises when I try to publish a new measurement using mosquitto_pub. The command runs smoothly but the entity in Orion does not get updated. Accessing Orions DB (mongo) I can check that the entity was created successfully but it has an empty value. Moreover, checking the logs yields the following:

mosquitto | 1559157902: New connection from 10.150.150.173 on port 1883.
mosquitto | 1559157902: New client connected from 10.150.150.173 as mosqpub|28750-mqtt (p1, c1, k60).
fiware-iot-agent | time=2019-05-29T19:25:02.374Z | lvl=DEBUG | corr=2c8aa6e3-faab-4166-9e20-0b362c165939 | trans=2c8aa6e3-faab-4166-9e20-0b362c165939 | op=IoTAgentNGSI.MongoDBGroupRegister arams ["resource","apikey"] with queryObj

| comp=IoTAgent
fiware-iot-agent | time=2019-05-29T19:25:02.381Z | lvl=DEBUG | corr=2c8aa6e3-faab-4166-9e20-0b362c165939 | trans=2c8aa6e3-faab-4166-9e20-0b362c165939 | op=IoTAgentNGSI.MongoDBGroupRegister elds [["resource","apikey"]] not found: [

] | comp=IoTAgent
fiware-iot-agent | time=2019-05-29T19:25:02.382Z | lvl=ERROR | corr=2c8aa6e3-faab-4166-9e20-0b362c165939 | trans=2c8aa6e3-faab-4166-9e20-0b362c165939 | op=IOTAUL.Common.Binding | srv=n/a | essing device measures [/apikeymia/motion003/attrs] | comp=IoTAgent
mosquitto | 1559157902: Client mosqpub|28750-mqtt disconnected.

(sorry about the format, first time asking and I couldn't find how to format the code section)

after each try of publishing a new meassurment.

Any help would be appreciated