it is not for adding cards on flipkart.flipkart started charging this offer handling fee long time ago,probably like 1year.The charge is levied on those cards on which some offer is ongoing.Suppose, there is a offer of flat 2000rs off on Realme P1 pro 5g on ICICI Credit Cards,then this offer handling fee will be levied on icici cards not on other bank cards.This charge may be account specific.