I think Igst is not applicable , Because RCM is applicable only on Intra state supply " It is pertinent to note here that the provisions of Reverse Charge under Section 9(4) are applicable only for supplies within the same state. The provisions of Reverse Charge under this Section are not applicable to Inter-state supplies as inter-state supplies cannot be made by unregistered suppliers."
Section 9(3),says, service or goods purchase from registered dealer but tax liability on service /goods recipient, not say about Which tax liability, place of supply defined the which tax liability. Please refer section 12,of IGST and section 10 under IGST