Invoice number is 1+ the quote number

Why is it when a quote number is 004-for example-the number of the invoice generated is 005 even thu i don’t have a 004 invoice? and when i try to manually change the invoice number to match the quote i get a message that this invoice number already exists.

In v4 invoice and quote numbers need to be unique, you can workaround this by setting either an invoice or quote number prefix on Settings > Invoice Settings.