My postcode is correct according to the Royal Mail website, but is not recognised by your system. Websites that link to you don't recognise my postcode either of course. What can be done?
It is difficult to help when we don't even know which postal code we are speaking of. In any case GeoNames has only the first part of the British postal codes.
Sorry - more information: my postcode is a UK one, and is OX26 6YD. I used to live around the corner and my postcode there was changed from OX6 6YE.
An example: to use the LinkedIn Search tools I have to use the OLD postcode from around the corner which is recognised by their site but by noone else including the Royal Mail, because the search tools don't recognise the new one which has been in place for around 7 years.
There was a bug in the webservice that made it fail to extract the outward part if it had four letters. We have fixed this error but no linkedin it is still not accepted. It is possible that they have a cache and it will work in while or the other explanation is that they have another mechanism to validate postal codes.