As long as an invoice is saved under "unprinted invoices" it will be considered a temporary draft. If you delete the invoice, its number will be released and reassigned to the next invoice. Therefore, you can always delete a draft invoice and recreate it: the assigned number should remain the same.
Once an invoice is finalized and saved as "outstanding invoice", its number will no longer be available. If you delete one of these invoices, you can either credit the amount (Credit Note) or delete it. You will see the message pictured on the right.
For transparency reasons, it is often advisable to credit the amount. There may be cases where a credit note does not make sense.
Let's assume you create and send a retainer invoice for a new client. Should this client change his mind and retain the services of another lawyer, you may as well spare the effort of creating a credit note and just discard the invoice.
Even under German compliancy rules, it is not necessary to have a continuous numbering for all invoices. However, each number may only be assigned once.
In the above-mentioned example, in order to ensure internal traceability, you may want to create a PDF copy of the retainer invoice and add it to a case memo. You will find the invoice in your document archive.
You will find more information regarding accounting here.
Go to "Settings", "Parameters", then select "Finances". You can modify the invoice number under the tab "Receivables". You may want to increase the starting number if you do not want to disclose the actual number.
You can also access all the "recycled" invoice numbers. Usually, there is no necessity to manage these manually, as timeSensor LEGAL does this automatically.