Under "Settings" (in the PamBill Dashboard top right corner) select the option "Reset account". This option will then delete all invoices and customers and restore the account to its original state (but your personal data/settings will not be deleted).

You can then also set the format of the invoice and customer number again (once). After the first import, this is then no longer possible.

Through this function you can test the order imports and adjust accordingly. If then everything is set as you imagine, then it can start with the real operation.