Protocol Error

[infinitemind2]

Using a Rockblock 9603 with a ItsyBitsy M4 powered by 5V supply. it all appears to be working but I constantly get 'Protocol Error'
Debug diagnostics of the transmission below:

AT+SBDWT
Waiting for response READY

<< ..AT+SBDWT
READY

Test message from Test code

Waiting for response 0

OK

<< ..Test message from Test code
0

OK

AT-MSSTM
Waiting for response OK

<< ..AT-MSSTM
-MSSTM: 712a957d

OK

AT+SBDIX
Waiting for response OK

<< ..AT+SBDIX............................................................Add to Failures
Tried to send message but returned error: Protocol Error
Tried to send message but returned error: Protocol Error
Upto retry: 4

Have not been able to send a message at all from this setup.
Have sent a message or two from another setup using a Adafruit Feather M0, do get a similar error.

[infinitemind2]

the last retry still didn't send but did get a different message sequence

.>> AT+CSQ
Waiting for response OK

<< ..AT+CSQ......
+CSQ:1

OK
internalSendReceive

AT+SBDWT
Waiting for response READY

<< ..AT+SBDWT
READY

Test message from Test code

Waiting for response 0

OK

<< ..Test message from Test code
0

OK

AT-MSSTM
Waiting for response OK

<< ..AT-MSSTM
-MSSTM: 712ab1f2

OK

AT+SBDIX
Waiting for response OK

<< ..AT+SBDIX..................................
+SBDIX: 32, 3, 2, 0, 0, 0

OK
SBDIX MO code: 32
Waiting for SBDIX retry...
............................................................>> AT-MSSTM
Waiting for response OK

<< ..AT-MSSTM
-MSSTM: 712ab413

OK

AT+SBDIX
Waiting for response OK

<< ..AT+SBDIX....................
+SBDIX: 32, 3, 2, 0, 0, 0

OK
SBDIX MO code: 32
Waiting for SBDIX retry...
............................................................>> AT-MSSTM
Waiting for response OK

<< ..AT-MSSTM
-MSSTM: 712ab5e6

OK

AT+SBDIX
Waiting for response OK

<< ..AT+SBDIX..........................
+SBDIX: 32, 3, 2, 0, 0, 0

OK
SBDIX MO code: 32
Waiting for SBDIX retry...
............................................................>> AT-MSSTM
Waiting for response OK

<< ..AT-MSSTM
-MSSTM: 712ab7db

OK

AT+SBDIX
Waiting for response OK

<< ..AT+SBDIX....................
+SBDIX: 32, 3, 2, 0, 0, 0

OK
SBDIX MO code: 32
Waiting for SBDIX retry...
............................................................>> AT-MSSTM
Waiting for response OK

<< ..AT-MSSTM
-MSSTM: 712ab9ae

OK

AT+SBDIX
Waiting for response OK

<< ..AT+SBDIX............................................................Add to Failures
Tried to send message but returned error: Protocol Error
Tried to send message but returned error: Protocol Error
Upto retry: 5