GST refund for wrongly paid tax arises when supply classification later changes; claim must be filed within the prescribed time. Tax paid under an incorrect GST head due to supply misclassification (inter State vs intra State) is refundable where the taxpayer pays tax under the correct head; 'subsequently held' includes reclassification by the taxpayer or by tax authorities in any proceeding. The two year limitation for filing the electronic refund application is measured from the date of payment of tax under the correct head, or from the notification date where payment preceded the notification. Refunds are barred if tax has been adjusted through issuance of a credit note.