Electricity Charges - GST?

Whether GST applicable under composite supply of service for electricity?

For instance,

If EB bill named in the firm A for which firm B(which is under the place of firm A) firm B is gives rent for use of land and energy.

however, electricity is consumed by both firms, in such case should Firm B has to pay electricity charges for their consumed units directly to EB Dept? or they must pay to firm A

if firm A receives whether GST applicable for such?

invoice not raised for the above.

what is the GST implications for the above?

Thank you!