It's indeed a bit strange that only some European countries can be chosen (not even all EU countries). In addition, it's strange that they need an address at all.

I'd use a random address, e.g. NS headquarters: Laan van Puntenburg 100, 3511 ER Utrecht, Netherlands

@moderators:

1. Why is an address needed?
2. If an address is needed, then why is the country selection so limited?

Hello Ericson, welcome on the NS Community forum!

We must check your address to comply with European privacy laws. I advise you to contact the NS Customer Service. They can add your address manually to the system.

@rvdborgt I don't know why the country selection doesn't include all countries. However, I do understand that this can lead to inconvenience for foreign travelers. I'll make an internal report, so that the responsible department can look into this.