Location of supplier of services determines place of supply under GST-prioritise place of business, fixed establishment, then residence.
Location of the supplier of services determines place of supply under GST/IGST by a hierarchical rule: (a) location of the registered place of business; (b) location of the fixed establishment when supply is made from another place; (c) location of the establishment most directly concerned where multiple establishments are involved; and (d) otherwise the usual place of residence of the supplier.

Location of recipient of services determines place of supply; prioritise registered business, fixed establishment, most concerned establishment, then residence.
The location of the recipient of services is determined hierarchically: (a) the location of the registered place of business where the supply is received; (b) if received at a place other than the registered place, the location of the fixed establishment elsewhere; (c) where received at multiple establishments, the establishment most directly concerned with receipt; and (d) if none of these exist, the usual place of residence of the recipient. The IGST Act contains the same hierarchical definition.