SAC Code for NGO

A medical society Non-profit organization. registered under Section 12A of the Income Tax Act. Receiving membership fees from members, and this membership fee is subject to GST as well.

This Month they organise conference and delegated responsibility for coordination, participation fees, meeting expenses, and so on to an event management company.

The Event management agency now needs to pay the excess amount to society in accordance with the agreement, and the said agency requires an invoice in order to do so. TDS will be deducted under 194 C as well.
Query:
1. Does the society need to issue an 18% GST invoice?
2. Applicable SAC code Number?