BGS2 Invalid Index Error response to ^SIST command | Telit Cinterion IoT Developer Community

I am testing the operation of the Transparent TCP Listener

Once this is in the Up state, I get the expected urc when an incoming connection is received:

^SIS: 0,3,0,"192.168.27.3:58148"

When I issue an AT&SIST=0 command to enter transparent access modem, I receive the following response:

AT^SIST=0

+CME ERROR: invalid index

However, the index is the srvProfileId in the urc, so this is not behaving as I would expect.