Hi @Rudasingwa,
This error might have been caused by various reasons.
To find the exact reason, select the cell where you have entered the formula.
A yellow caution symbol would be displayed beside the cell.
Select that icon to see what the exact issue is.
I have also attached a support link below that might help with your request.
support.microsoft.com/en-us/office/how-to-correct-a-spill-error-ffe0f555-b479-4a17-a6e2-ef9cc9ad4023
Do not hesitate to reach out if you need anymore support.
Regards,
