GSTIN of the recipient must be provided to airline or hotel who will issue their invoice and file their GSTR-1 citing this GSTIN and credit will flow to the recipient, subject to section 17. Accordingly, travel agents who issue a consolidated invoice are causing loss of credit of taxes paid to airline or hotel and merely passing on credit of their taxes (5% as tour operator and 0.9%/1.8% on ticketing).
(ICAI FAQ PUBLICATION 06-09-2017 : Exemptions on Supply of Services – FAQ NO. 38)