About the SMS category

The format of messages can be either PDU mode (entire TP data units used) or text mode (headers and
body of the messages given as separate parameters).

The command to switch to textmode should be AT+CMFG=1. After sending it I got error. In the documentation there is no description as a command. Any hint is welcome.

My firmware is:

AT+CGMR
SECURITY,V100R100C10B657SP3
PROTOCOL,V100R100C10B657SP3
APPLICATION,V100R100C10B657SP3
SEC_UPDATER,V100R100C10B657SP3
APP_UPDATER,V100R100C10B657SP3
RADIO,BC95HB-02-STD_800
OK