More accurately described as a colloquial phrase, it means
"your deserved reward or just due" for an action taken or statement you have made. It always conveys that to be of a negative nature. It should be hyphenated as neither word, of it's own definition, conveys close to the meaning of the combination of the two; therefore the linkage of the hyphen is needed.
"Joe has always bragged that he was the team's best batter, but in the playoff game he went 0 for 4 and humiliated himself."
(Joe; therefore, got his just due or his come-uppance for his continual bragging and then, his abysmal failure.
A punishment you deserve for doing a bad thing
You're a cheating git.
One day you're going to get your come-uppance.