Hello,

InvoiceOcean allows you to change the format of invoice numbering, in order to do this navigate to Settings > Account settings > Invoice numbering > Default format of invoice numbering and select your preferred option. Whenever you create a new invoice the new numbering format will apply to all new invoices, the old invoices will remain unchanged, but can be changed manually. To go back to the default settings, repeat the process.

Kind regards,
Bagi