u/xix161

Hello everyone! I'm going to be traveling through Europe this summer (first time out of the USA) with a Eurail pass and currently getting everything in order. I want to make certain train reservations as soon as possible (London -> Brussels for instance) but the booking sites ask for my passport number, which I am still waiting to receive (I've already applied and everything, but it can take some time). Is it possible to reserve a train without the passport number and add it later? Thank you all in advance, this subreddit has been super helpful for planning my trip!