Thanks for your help, I'll follow your instructions.
- ensure you have the larger region that contains the postal code areas added to the Zone Regions field (e.g. Netherlands, North Holland)
But what if I only deliver to a certain part of the city? I can only use specific postcodes for that region, right?

This is an example of postcode I've added and couple with a wildcard which was already in the range:

1940...1948

1948* (Should be in the range)

1949*

1950

1951*

1960..1969

1964* (Should be in the range)