Do you use the command AT+NBAND first? Check whether the frequency band is selected correctly, and then check AT+CFU in the command? With AT+CGATT? Are all set to 1
Do you start with the instruction AT-NBAND? See if the band is selected for the right, and then view the AT-CFU in the instructions? With AT-CGATT? Whether they are set to 1.
You use the command at + nband first? Check whether the frequency band is selected correctly, and then check at + CFU in the command? And at + cgatt? Are they all set to 1