igst or cgst/sgst

if in mumbai u dnt have any place of bussines which statisfied the condition of Section 2(85)

second if ur case does not satisfied the conditions under section 2(15) for location of supplier

then location of supplier is mumbai

and as per section 12 of igst act place of supply will be mumbai


then it will be interstate supply
and u will charge Igst in the bill

you are not required to take registeration in the state of mumbai

just raise igst invoice