Cannot set USBCFG=4 with Telit and LTE-M sim card

Although SIXFAB core shows an active cellular connection I keep getting an error message when trying to set USBCFG to mode 4:

AT

OK

AT#USBCFG?

#USBCFG: 0

OK

AT#USBCFG=4

ERROR

Some more commands I have tried:

AT#PORTCFG=?

#PORTCFG: Variant=0: AT= USIF0 USB0 USB1

#PORTCFG: Variant=3: AT= USIF0 USIF1 USB0

#PORTCFG: Variant=8: AT= USB0 USB1

#PORTCFG: Variant=13: AT= USIF0 USB0

OK

AT#USBCFG=?

#USBCFG: (0,3)

How can a troubleshoot this further?

Kind regards,
Arjen