I know postcodes
I am trying 34718. I want to show there is no difference
I know it sounds like a dumb question, but did you select "Turkey" as Country (first field) before trying to put your zip code?
I tried your zip code (34718) while the country was Brazil (my country) and it was giving me this error (because it's not in my country's format), but when I selected "Turkey" it worked without giving any error message.