Refund of wrongly paid tax: taxpayers can claim when supply classification is subsequently found different, subject to procedure and time limits. The term subsequently held includes both taxpayer-initiated reclassification and reclassification by tax officers, and refund claims must be filed electronically within two years from the date tax was paid under the correct head, with earlier correct-head payments governed by two years from the date of the relevant notification; refunds are excluded where adjustment was made by issuing a credit note.