In your Invoices tab, you will notice the different status's of each invoice.
Status codes:
Imported - Synced to Paidnice, but has not met late fee criteria, yet.
Frozen - Manually or conditionally (via penalty settings) frozen and will not issue any penalties, unless conditionally this changes, or is manually processed.
Penalty Issued - Late fee has been issued.
Job Failed - Processing job has failed (if this happens contact support)