Most probably you didn't have a valid ticket. For instance because you didn't check in, you checked in with another trainoperator, you travelled 1st class with a 2nd class ticket, etc.

No, I did. 

I don't speak Dutch so I didn't understand what he meant.

If you really don't know you can best call the customer service. Without proper information we cannot help you here.

This is the number of the fine 

L51****

Edit by moderator: personal data

Can I get the number? 

We cannot help you here, only customer service can.

030 7515155 is the number of Customer Service, but they cannot check a fine right away. You may try it at least a day after you got the fine. 

I don't speak Dutch so I didn't understand what he meant

Train conductors do speak English in general.

Hi samiyosefnl, and welcome to the NS Community!

What a shame you have received a fine while travelling with us. As Tamzin states there can be several reasons you did not have a valid ticket, but this is the most notable reason to receive a fine.
I'm afraid it's not possible for us to check the fine for you, but Customer Service can. You can find them here. 

It's good to keep an eye on what Thom said as well. My advise is to wait until you have received the letter of payment at the address you've given the conductor. That way you are sure the fine has been registered in the system and Customer Service can help you with your questions.

Thanks for your quick reply

I got a fine (boete) and I don't know what the problem is? 
 

I had a valid card. 
I checked in. 
I travelled with a 2nd class. 

The money withdraw from my account.

Better not share personal details here.

But it looks like you did pay for a journey. The best is to call customer service now. They can also see you paid for a journey.

Thanks a lot. 

@samiyosefnl,

The NS fined you for the journey from Leeuwarden to Heerenveen.

Your screenshot is for the journey from Heerenveen to Leeuwarden. What does your account say about the trip from Leeuwarden to Heerenveen?

It is best to remove your address and chip card number. Either black it out or remove the screenshots. 

You probably did not check in at NS at Leeuwarden, got a fine, and checked outat Heerenveen. It is likely you checked in with Arriva, not NS at Leeuwarden. But I am guessing, your travel history will tell. Calling Customer Service is a good idea. A first fine may be cancelled. 030 7515155.

I did (check in) But conductor told me don't

( check out) and gave me a card to use it when check out. 
This is why there is no (check out) But there is proof that I did (check in) 

Looks like you checked in with Arriva in Leeuwarden. There are gates for NS and Arriva on that side of the station. 

With af fine you can always check out. Maybe you used your chipcard at Heerenveen, not the fine. Calling Customer Service is wise. They can reproduce it.

It's most likely you checked in at an Arriva gate and not at an NS gate just as I already mentioned in my very first answer. When the conductor inspected your ticket he then noticed that you had no check in for NS.

Thank you all for the tips and information.

The screenshot clearly shows a check-in at Heerenveen with NS (there is no Arriva in Heerenveen)

So why did the conductor give you a fine (plus a card to pass the gates at Leeuwarden without having to check out)?

The fine was for traveling from leeuwarden to heerenveen. TS did not check in at Leeuwarden and because Heerenveen does not have gates the checkout there is interpreted as check in