I do not see the "Post reference" button in a KudoZ question. Why?

Once you have posted an answer to a KudoZ question you will not be able to make a reference post. This is so because it is assumed that you have put all the information in your KudoZ answer, making your answer a more useful resource, and ensuring that all relevant information is kept in one place.

It is possible to make a reference post first, and then propose an answer though.