Thanks for the reply.
In Sigfox backend DEVICE XXXX - Messages page
On this page if I look at the callbacks column I see two arrows per message. The right hand side arrow is red. If I click this it says Status:[INVALID_CONFIGURATION] Data(Hexa): N/A
In Sigfox backend DEVICE TYPE XXXX - infomation page
I see that it says the following:
Downlink data: From callback (No callback available)
I can see that there is a way to edit this (top right)
If I click edit, I can see that the unit is set to CALLBACK, (There is another option for DIRECT)
Serial terminal reports the following
Everything as in the example e.g.,
(ignoring first bit) ... then
Sending Hello World!
Getting the response will take up to 50 seconds
The LED will blink while the operation is ongoing
Could not get any response back from the server
Check you the SigFox coverage in your area
If you are indoor, check the 20db coverage or move near a window
Just tried it again. The message gets through to the Sigfox backend fine, but nothing comes back as shown by serial output.