Would you say kudos are due? You shouldn’t.
Kudos is a word of Greek origin originally meaning “praise and honour received for an achievement” and now also used in a looser sense to mean compliments or congratulations. It’s singular. You can only have kudos. Although some dictionaries recognise the singular form “kudo” as a valid back-formation, in reality you’ve either got kudos or you haven’t: you can’t very well have one kudo.
Actually, arguably, you can: kudo is the name of a Japanese martial art that combines karate and judo. Kudo is also an alternative (perhaps incorrect) spelling of kudu, a kind of antelope from eastern Africa that got its name from the Xhosa language via Afrikaans and means something like zebra-deer. But these words are nothing to do with kudos in the sense in which it’s usually used.
Kudos is due to you for not saying “kudos are due”.
You can read about the correct way to write kudo and a whole lot more, in the Clifford & Co editorial style guide.