REBATE RECEIVED FROM FOREIGN PARTY AFTER MAKING PAYMENT OF THEIR INVOICE.

AS WE IMPORT GOODS AND PAY IGST ON ASSESSBLE VALUE OF ACUTAL INVOICE (BEFORE DISCOUNT/REBATE). WE MAKE PAYMENT OF TOTAL INVOICE VALUE TO THE FOREIGN PARTY IN USD BY CONVERTING INR TO USD, FURTHER WE ISSUE A DEBIT NOTE TO THAT FOREIGN PARTY TO GET THE REBATE OR DISCOUNT AGAINST THE SQME INVOICE AND THEN WE RECEIVE THE PAYMENT IN FOREIGN CURRENCY AGAINST THAT DEBIT NOTE WHICH IS ISSUED FOR REBATE OR DISCOUNT AND GET INTO INR IN OUR BANK ACCOUNT BY CONVERTING USD TO INR. AS WE PAID GST ON ASSESSABLE VALUE OF ACTUAL INVOICE AND GET THE ITC ON IMPORT. FURTHER WE ISSUE THE DEBITE NOTE TO GET AMOUNT FROM FOREIGN PARTY AS A REBATE OR DISCOUNT , SO IS THAT REBATE OR DISCOUNT IS LIABLE GOR GST SEPARATELY OR NOT , BECAUSE WE HAVE ALREADY PAID AND TAKN ITC AS PER ACTUAL INVOICE. SO TELL ME THE SOLUTION AS PER THE ABOVE.