Can I pay with cash for the train from Oslo airport to the central station?
Next week I am travelling to Norway. To get from the airport to my hotel I will need to catch the train to Oslo Central Station. Can you pay by cash at the ticket machines or is it card only? If no...
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There are two different train operators serving the line from the airport to the central station:

Airport Express Trains (Flytoget) are usually departing every 10 minutes (x:06, x:16, x:26, x:36, x:46 and x:56), travel time is 22-25 minutes and a single adult ticket costs NOK 180. You can buy tickets from the ticket machines and pay with cash.

Suburban and regional trains operated by the state railway company NSB are usually departing three times an hour (x:09, x:39 and x:59), travel time is 26 minutes and an adult ticket costs NOK 92. Tickets for these trains can be bought with cash from ticket machines, but also from the NSB ticket office, which is open Mon-Fri from 7:00 to 22:00, Sat from 10:00 to 16:45 and Sun from 10:00 to 22:00.

All ticket machines at the airport accept both coins and bank notes (they are all indoor), but are often restricting the amount of change, so you may only be able to use the next larger bank note to pay for a ticket.

According to the website for the airport express train:

You can buy paper tickets from any of the vending machines installed at all our stations, including the arrival terminals at Oslo Airport. All our vending machines accept both card and cash payment.

So, for the airport train, it's clear that cash will be a possibility.

Here is some information on Oslo Central Station in English. It doesn't specifically mention whether the ticket machines take cash. But there is a ticket office open long hours. I have also looked at the page on buying tickets on the Oslo Central Station site with Google Translate, but it doesn't specify whether ticket machines take cash.

This page from the Norwegian rail company gives information on how to buy tickets. Translation via Google Translate:

Ticket Machine

On machine you can buy most train tickets and extract preordered tickets. At ticket machines standing outdoors [you can't] pay with banknotes, only cards and coins.

So at all ticket machines, you should at least be able to pay with coins. At some you can also pay with bills. I would expect the latter to be available at a major station like Oslo Central. But I don't see a definitive source saying that.