GST refund after huge credit note

I raised an invoice dated 30/3/23 for 20 lakhs including 18% GST. 31/3/23 was the last day of company operations. I have paid and filed GSTR1 and 3B by 20th april. Now customer is willing to pay only 5 lakhs and asking for 15 lakhs credit note. What will happen to GST I paid? As I will closing LLP, its like I can show loss in FY23-24 which is of no use and also paid GST. What are the options?