For security services , we have to pay gst under reverse charge Machanism not for all cases, so please refer Notification no 29/2018 (C.T.) rate dated 31/12/2018 .
GST on security services was applicable from 1st of July 2017 on forward charge but it has been brought under Reverse Charge Mechanism(RCM) from 1st January 2019 based on Notification No. 29/2018- Central Tax (Rate), dated 31st December, 2018.