In the case you have put it on an existing card, did you activate it at a ticket machine? 

I couldn't find how to activate it on the machine, so I went to the manual service desk. After swiping the card, the manual service desk will tell me that it is already in the card, so I can check in directly.  I don't know if this is already activated

When you ordered and got a new card, it must be activated. Did your subscription start already? Otherwise contact Customer service. English is spoken. 

20 euro’s may be withdrawn with Flex after a wrong checkin or wrong checkout. In the case you are traveling with Flex, this is not shown directly however.