GST REFUND - INVERTED DUTY STRUCTURE

As per section 54 of the CGST act, you have to apply for refund before expiry of two years from relevant date.

Ok thanks. but how to fill period when applying redund in GST portal?

Dear sir, If u r a monthly taxpayer, you can file combine refund application and if u r a quarterly taxpayer, you can merge quarter only.

Sir, please refer Notification no 13/2022 central tax iin which exclusion of time period 0f March 2020 to Feg 2022 as covid pandamic period for calculation of limitian period for filing application of refund, so on the basis of this notification shall I apply for reffund from FY 17-18? please advise.

No you can't also there is limitation period of 2 years .so, for period before 2 years application can't be filed.