Gst sac code for co-working space

DEAR sir,

we have 150 seats in our office space. and we do rent 1 or more seats to diffrent companes on rent which includes space rent,electricty, power back generator, internet, computers , internet, house keeping etc.on a fixed price lets say 6k per seat per month.

kindly advice which sac code we should mention on the bill.

my second question do we need to add first ths sac code before adding it to the bill? or can we use this sac code before adding ? thanks