@Amelia1430 wrote: ``I don't know what's going wrong``
And neither can we because you do not provide sufficient information.
At the very least, provide the formula that you are using. Copy from Formula Bar and paste into a response here.
Also, provide the data that the formula references. Numeric values should be displayed with 15 significant digits.
But ideally, attach an example Excel file that demonstrates the problem. Remove any private data (names, account IDs, etc).
Although sometimes the #NUM error simply means that you need to provide a "guess" to help the internal algorithm (but there is no easy way to determine a good "guess"), often the root cause is that the cash flows are not set up properly.
So, it might help us help you if you provide some context for the data that you provide.
What do the cash flows represent?
If they are derived from other data, it might help us help you to see all of the data, not just the data presented to the (X)IRR function.
