My error I left a semi colon in the formula
Try
=IFERROR(INDEX($A$2:$LZ$2,SMALL(IF($A$1:$LZ$1=$A5, COLUMN($A$1:$LZ$1)),COLUMN(A:A))),"")
You must commit with the insertion point in the formula bar. Curly braces will appear. You cannot add them manually

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