SUMIF function works on Sheet1 but not Sheet2

I have two sets of data, one set being located on Sheet1 ("Prepaid") and the other on Sheet2 ("Monthly"). They are in identical formats. They should use the exact same SUMIF or SUMIFS formula referencing Sheet3. The formula works on the Prepaid tab but on the Monthly tab only returns a value of 0.

Thanks in advance.
Bjordion

Maybe on the Monthly sheet the numbers to be added are text values which look like numbers. See what a SUM formula directly on the Monthly sheet produces.

Hope this helps.

Pete