This error message is shown then you are trying to book a shipment with a Pakjegemak service level and the 'house no.' field for the invoicing party is not filled. Please fill this field, you should then be able to book your shipment.
For further information about this service, please see the following article:
PostNL Pakje Gemak
Should you need further assistance with this issue, please do not hesitate to contact us at email@example.com and please send us the reference of the shipment that you're experiencing issues with.