Question 5 - Suppose a taxable person has paid IGST/ CGST/SGST mistakenly as an Interstate/intrastate supply, but the nature of which is subsequently clarified. Can the CGST/SGST be adjusted against wrongly paid IGST or vice versa?

Mistaken GST classification: refund is required under Section 77 rather than adjusting IGST with CGST/SGST.

A taxable person who has paid tax under the wrong GST head because of an incorrect interstate/intrastate classification cannot adjust CGST/SGST against wrongly paid IGST or vice versa; the appropriate remedy is a refund of the tax so paid under the statutory refund mechanism set out in the GST law, specifically Sec.77.