How to send AT+QCFG="band" for Band Configuration?

I am using the EC20 module
when i send AT+QCFG="band"1,0,0,1
Geting resonse +CME ERROR: 3
I need to lock the band for GSM.
please, help me with how to lock the band.





Thank you,

Are there any other steps before sending the AT+QCFG="band"1,0,0,1?

and also when I send the AT+QCFG=“nwscanmode”,1,1 // to lock the GSM Mode
every time I keep getting disconnected.

please let me know how to switch from LTE to GSM mode.

I suggest you start with AT+CFUN=0


why ?