Gst on security service provided by a pvt ltd co. to a co.op hsg socy

In your case, I am having two points 

1) As you adopted procdure ,  You have to issue Tax Invoice and pay GST under FCM , as far as society is consern, they will pay GST along with Invoice as they are unregistered, and Show as expenditure in Income & Expenditure A/c , in the books 

2) As per Notification 29/2018 dated 31/12/2018 , (please refer) Society has to pay GST under RCM if society is registered, so  my concern is , whether Society has to take compulsory registration under section 24(3) of the CGST Act pay GST under RCM , and show RCM entries in the books of accounts and file gst retun and do all prodcure after registration .

 , So  take more Opinion on this and please refer notification , as mentioned above. 

Follow sec 22 of cgst act