An advance payment is unearned per se, they didn't work for it, they were just given it. Why reiterate that is is unearned?
The way I understand it is that somebody is given an advance payment but did nothing to earn it afterwards, for example it says here
"...for failure to promptly return unearned advance payments of fees after Hammond did not take reasonable steps to advance Mrs. McBratney's case."
Otherwise it is a fine example of tautology.