Hi @Britney Starr,
What error message you got? Kindly share here and it is important for us to help you troubleshoot.
Generally, we can get this like the following screenshot. I got the sum of A1, B1 and C1 of Sheet1 in the A1 of Sheet2. Is there any difference between your action and mine?
Also, have a try to directly apply the formula to the cell instead of mouse-clicking and enter-pressing. In my example, if I copy the formula =SUM(Sheet1!A1+Sheet1!B1+Sheet1!C1)
and apply it to the Sheet2 A1 cell, it also works.
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