The GP88S does not support narrowband (12.5kHz) natively in all firmware versions. Late-model radios (firmware R05.xx.xx) do, but older ones require a firmware upgrade which is a separate, more dangerous procedure.
You cannot use a generic USB cable. You need a or a RIB-less clone cable specifically wired for the Spirit/GP88s series. motorola gp88s programming software
The confusion surrounding the software usually stems from Motorola’s naming conventions. For the GP88s, the software you are looking for is often labeled: The GP88S does not support narrowband (12