Place of supply: where embarkation is unknown at issue, default rule under IGST applies to domestic travel tickets. Where a domestic 'anywhere' travel ticket is issued in advance and the place of embarkation is unknown at invoice issuance because the right to passage is for future use, the place of supply cannot be the place of embarkation and the default rule under the proviso to section 6(10)(b) of the IGST Act applies.