Different business verticals

Since the GST registration is only for the trading business in hardware items, you should not account for the service income from cab services in GSTR-1.

GSTR-1 is used to report supplies (sales) related to the registered business, which in this case is the trading business.

 The cab services are a separate business and require a separate GST registration.

Since they are under the same PAN, your client should consider registering the cab services under GST as well.

 If your client wants to consolidate both businesses under a single GST registration, they can apply for a separate GST registration for the cab services or opt for a single registration for all businesses under the same PAN.

However, currently, you should only report the trading income from the hardware business in GSTR-1 and maintain separate records for the cab services. Consult a tax expert or the GST helpdesk for further guidance.