The automatic designation of all the Contracting States party to the EPC at the time of filing of the European patent application is effected by the filing of the application, whereas the designation fee may be paid later (see A-III, 11.2.1).
Payment of the designation fee covers all the Contracting States, except those States the designation of which has been expressly withdrawn.
Art. 2(1), No. 3 RFeesArt. 6(1) RFees
Such payment simply needs to be marked "designation fee" in order for the purpose of the payment to be established.