place of supply

my client supplied machinery to a party at Rajasthan under IGSTfrom Telangana. Their scopebof supply includes free installation and commissioning. However, the installation and commissioning contract was given to a person at Rajasthan. my query is what's is place of supply for this service contract. we are telling them to raise IGST invoice being provided to registered person. But their consultant is of the opinion that they have to give only Local invoice only as the service relates to immovable property. kindly clarify