Whether a registered person who has paid IGST on a transaction considered by him to be an inter-state supply, but which is subsequently held to be an intra-state supply is required to pay interest

No. Such registered person shall not be required to pay any interest on the amount of CGST and SGST or CGST and UTGST payable, as the case may be.

(ICAI FAQ PUBLICATIONS 06-09-2017 Tax wrongfully collected and paid to Central Government or State Government : FAQ NO. 38)