„Unfortunately tickets for today are sold out. Tickets for the day are released daily on our website at 9:00. (I arrived at 9:50). It is not possible to buy tickets at the museum.“
This reminds me of the scene at the Auschwitz entrance, totally different from at Birkenau, walking distance away.
Pro tip: there are Holocaust sites in Europe where you don’t need to buy a ticket and stand in line.