This command requires a column header. You should include the column header
for column M in the source range as well as the copy_to range.
Assuming your header for M is in M5 it will put the header in B5 followed by
the unique results under it.

Range("M5:M200").AdvancedFilter Action:=xlFilterCopy,
CopyToRange:=Range( _
"B5"), Unique:=True