The AT^SM20 and AT^SSYNC commands cannot be issued on the same command line.

ADDITIONAL INFORMATION:

The AT command set documentation indicates that multiple commands can be combined on a single line.

AT^SM20=1 yields OK response
AT^SSYNC=1 yields OK response

But:

AT^SM20=1^SSYNC=1 yields ERROR response
AT^SSYNC=1^SM20=1 yields ERROR response


RESPONSE:

If you want to add these two commands together in one command sequence, then use a semicolon to separate the commands. Example: AT^SM20=1;^SSYNC=1