@illinilass starting looking at dates in the next couple of weeks for October but you could always risk just turning up and scan the QR Code that is just inside the entrance. Although we booked we ended up being 4 hours late so rebooked using the QR code. You will also need to book if going up the Sky Garden. They are booking now for October. It a building that is now dwarfed by Horizon 22 and has the same views. https://tickets.skygarden.london/WebStore/shop/viewitems.aspx?cg=SkyGarden&c=Tickets