Here is where I am at the moment when I follow the howto on developer.puri.sm
root@pietro:~# mmcli -m 0 --simple-connect=" apn=mobile.bm"
error: couldn't connect the modem: 'GDBus.Error:org.freedesktop.libqmi.Error.Protocol.CallFailed: QMI protocol error (14): 'CallFailed''```