This is the Authorization key. You have to add it as a GET parameter.
Your auth key can be found on the [CMS](https://www.pro6pp.nl/cms).


authKey

This will return all postal codes within a range of a given postal code or city.

* Either the `postalCode` or `settlement` is required


The address's postal code which can be up to five digits long


postalCode

The address's settlement (city, town, village, or hamlet)


The range to search, in meters. Maximum 100000.


The amount of results returned, a number between 0 and 999.


Return German postal codes within range of a given postal code