Queensland regulations say that a licensed gasfitter must provide the certificate at the completion of their work and that the customer must supply a copy of the certificate to the gas supplier (Hotgas) prior to the first delivery of LPG. (See Petroleum and Gas (Production and Safety) Regulation, 2004 Sections 91,92)
Hotgas also recommends storing your certificate safely in case you need to make an insurance claim or for production to a new owner upon sale of the premises.