Downlink to end node question

Hello all.
I have an end node built on a proprietary pcb. I am using CayenneLPP in the firmware. I am experimenting / trying to correctly download a simple message from TTN to the node to turn on an LED.
To do so I go into Messaging section of the node (on TTN) and under Downlink tab I keep the switches the same, select the port I am using to decode and just enter some bytes (currently random as I am just trying to see if I can rcv packets). I then “Schedule the downlink”. I never see this downlink show up on the live data of the gateway. I get the following live data message on the node itself. I also set a breakpoint in the firmware at the beginning of the receive function (which is copied from working code that I experimented with on another board) and I never break.

I have chosen CayenneLPP in the payload formatter for both downlink and uplink but beyond that I am not sure how to proceed…Any help appreciated.



resulting in:


I am using CayenneLPP…The randomness was just putting bytes into the message. I do not completely understand the packet structure so ‘my hope’ was to have my C function receive the message and from there I could get an idea on how to treat it within the code to produce an action.

I found that if I configure the payload formatter to CayenneLPP using the tabs on the left side of the screen that the error seems to have gone away. Prior to this I was selecting the node itself by clicking on it then using it’s tab to set the payload formatter. This method yielded the error you are looking at.

So to get back on track I no longer see the error mssg within the node activity see below:

payload is random until I can prove I can receive mssgs:


My gateway (using TTN console) never seems to show the message queuing am I missing something?

The LNS will pick the most suitable gateway, it may not be yours.

There isn’t much engineering going on when you put random bytes in instead of the prescribed format, which you say you do not complete understand - it’s well documented as a channel number, data type and then the data values.

And turning features on & off to make error messages go away without understanding why is equally un-engineering like.

I’d turn off all the Cayenne so you can get the raw data through to the device which you can add a serial output of the bytes received in a downlink. Then take it from there.