it is an array formula
enter it with control-shift-enter instead of just enter

"Richard Fangnail" wrote:

I don't understand what it means if you sent MATCH two arrays. The
below is from the Help page for "count unique values among
duplicates":

=SUM(IF(FREQUENCY(MATCH(B2:B10,B2:B10,0),MATCH(B2: B10,B2:B10,0))0,1))

MATCH is usually sent an array and then a value.