If approval is enabled, there are two configuration options with different implications for accounting. Configuration is done here: General Configuration. Also refer to Approval.

Approval (Warning)

If approval is enabled and configured as "Warning", there will be a message when a report contains work logs without approval and the report was created with "Prepare charging work logs" checked:

However, it will be possible to charge the work logs and create the invoice.

Approval (Manadatory)

If approval is enabled and configured as "Mandatory", there will be a message when a report contains work logs without approval and the report was created with "Prepare charghing work logs" checked:

The button "Charge Work Logs" is not usable. It won't be possible to charge the work logs and create the account. You need to get approval, or you can exclude work logs without approval from the report (see Charge Work Logs - Create Invoice).