Hi Poryvaiev and welcome to the Community! 
We can only help you in Dutch or English. I am sorry to read that you got a fine. Please contact our costumer service so they can help you with this. 

One more thing: You can only buy a ticket with Dal discount if you have the subsription for it. It's not allowed to just buy a ticket with a 40% discount without additional subscription.

And what kind of subscription is that? So where can I subscribe to it? And another question - will I have to pay anyway? And where to do that?

Have a look at this page: https://www.ns.nl/en/nsflex/webshop#/bestelling/producten/2

Hope that clears things up a bit!

I can't tell you if you have to pay this fine. That depends on what kind of ticket you had. Our costumer service can tell you that. 

Beside that, I think you bought a ticket with Combined Travel Discount. You can only travel with this ticket if you travel with someone who had a subscription with NS. 

I have NS account  and bought ticket via NS app

Choose that price Foto as an example

But so many thanks for your support

Oothanks 

i wiil by this item and travel without same problem in future🥳🥳