It's ok if you don't have the GST number or other needed Tax id. If you have, then please mention it there else leave it.
GST number is used in case you use ExparaBiz Invoicing Software for the Invoices being generated by you for your vendors. It is always good to add your Tax ids. If the Tax ids are not supplied in the company details, you won't get to see it in the invoice that is generated.
