How to get the Device Registration PIN from Murata module using I-CUBE-LRWAN?

I'm using the Discovery Kit B-L072Z-LRWAN with the expansion package from ST (I-CUBE-LRWAN), but I need to get the Device Registration PIN from the Murata (manual) module in order to register the device in my LoRa-Cloud account.

I am aware that the manual describes how to do that via UART, but I tried and I couldn't get any response from the board.

Any help is more than welcome!

Thanks in advance!!