GST Invoices Series

As you have a single GST registration (GSTIN) in your name (Sourabh Katiyar), you can use the same GST number for both services:

1. Security services (M/s Katiyar Sec Services) 

2. Rental income from commercial space (Sourabh Katiyar) However, you'll need to maintain separate records and accounts for each business activity. 

Since both services are under the same GSTIN, you can use the same GST number on both invoices.

 For invoicing, you can use different invoice series to distinguish between the two services.

 Here's a suggestion: -

Security services (M/s Katiyar Sec Services): Use invoice series "SKSS-XXXX" (e.g., SKSS-0001, SKSS-0002, etc.) - Rental income (Sourabh Katiyar): Use invoice series "SKR-XXXX" (e.g., SKR-0001, SKR-0002, etc.) This will help you maintain clarity and ease of accounting. 

Additionally, ensure you're charging the appropriate GST rates for each service: - Security services: 18% GST (if you're providing services to a registered person) - Rental income: 18% GST (if the rent exceeds ₹20 lakhs per annum)