If an invoice has been paid (Balance is 0.0) but the status is still 'Overdue' or 'Unpaid', it might be because of the system's rounding off to 2 decimal places.

You can fix invoice status by adjusting the rounding threshold within Account Settings:

The Invoice module within the Account Settings page has a Payment Rounding setting:

The decimal place rounding setting would look like this where setting:

1 = 0.0

2 = 0.00

3 = 0.000