Rak5860 AT sequence

Dear All ,

someone have the AT Commands sequences for connecting in vodafone NB-IOT . I’m going crazy, but it doesen’t connect .
The Vodafone customer care told me that is mandatory activate the roaming for connection , i use this command but it answer always ERROR :

bg77_at(“AT+QCFG=roamservice,2”, 500);

Thank you for who will help me .