As long as you have not downloaded or viewed the ticket, it should be refundable.

Maybe one of the Moderators can help you, or you can get contact with the NS Customers Service with this link: https://www.ns.nl/klantenservice/contact

I'm not sure how it's supposed to work (I've never bought a ticket via the app) but the app doesn't say how the ticket will be delivered, which implies to me that it should be visible in the app after buying it. If NS expects people to look in their e-mail, then I think they should mention that in the app.

E-tickets are always delivered by e-mail, with a link to download or import them in the NS app.

An exception seems to be the Jongeren Dagkaart (12-18 years off-peak ticket), which can be ordered directly as an in-app purchase.

The app is indeed quite limited in the information you get when ordering an e-ticket (check your e-mail for instructions).

Thank you very much for your help.