Only Dutch organizations are required to register with a valid registration number. The platform is linked to the  Dutch Chamber of Commerce website which automatically generates the organization data.

As a foreign organization it is possible that you do not have a registration number. 

To register successfully, enter a fictitious number, letters or a combination of these in the 'Registration Number' field.

Click on then Search and Verify, you will see that you can enter other details of your organization.

You can register your organization.