I don't know the ISBN of the publication. What next?
It is always worth trying to find this out. If no ISBN is known to us, the publication automatically falls into the ‘other book’ category, which has consequences for the amount of any associated collective rights.
You can try to find the ISBN via this link in the catalog of the Royal Library: https://www.kb.nl/
If a book does not have an ISBN, you cannot submit it online, but you can use the book submission form https://pictoright.nl/app/assets/Pictoright-Opgave-Boeken.pdf, provided that it is for sale and has a minimum print run of 250 copies.