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Using Index/Match Between Two Sheets Returns #SPILL

I’m working in a spreadsheet that contains two sheets. Sheet 1 has a table that contains rows of Purchase Order numbers and columns for each month that house financial data below the headers. The table was imported from another Excel workbook.

Sheet 2 has a column of Purchase Orders that are listed in a different order than Sheet 1, so I am using Index/Match to rearrange the data. I used the formula below, but it just returns the #SPILL error. I’ve spent a couple days working on fixes and can’t seem to get anywhere.

=INDEX(Sheet1[23-Apr], MATCH(Sheet2!A:A,Sheet2[PO'#],0))

Greatly appreciate any help. Thanks.