You mistyped the number; the last two digits are in reverse order.
More importantly, if you bought NS Flex Dal Voordeel voor 5.60 euros, you don't need to top up. You can just check in and out with the card and will get an invoice at the end of each month for the travel costs incurred, which will then automatically be withdrawn from your bank account.
And just to be clear: judging by the expiration date of the card you ordered NS Flex for existing card, in which case you will need to load the NS Flex season ticket onto the card at a ticket machine for it to be active. This is mentioned in an email you should have received.
I can’t see the (removed for privacy) photo but you can activate NS Flex at any service point (e.g. at a nearby store). Choose ‘pick up order’ (bestelling ophalen) and follow the instructions on the machine.