EXPORT FIRM MATTER - Goods and Services Tax - GST

Dear All, An export firm filed returns of 2022-23 under rate of 12% instead of 18%. The GSTR-1 invoice filed was under IGST Paid and as such the refund of same amount was received @12% only. The firm came under GST Audit by dept. and now the AO is asking to pay the difference of 6% of IGST tax as it was not correctly shown at the time of filing GSTR-1 . Issue is now what will happen to the tax amount if paid now ? As no revenue loss to Govt. in this matter as IGST was less paid and same amount of refund was received. Please suggest in the matter and suggest remedy as per law if any.