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