Hi RoyTi
Thanks for your post. The invoice number is automatically generated, based on the last number you used. If you use quotes it will use the same sequence as the invoice numbering. If you change the invoice number, you’ll change the automatic numbering. For example, if you change the number to 000081, the next time you create an invoice, the new invoice number will be 000082.
As for the duplicate invoice numbers not giving you a warning, this is something we are aware of and our team is currently investigating.