I will try it.

Yes, I understand. But I want to give the possibility to the admin of the software to check the invoices...

- in finance settings, you can activate performa invoice option, so if you create invoice directly, or from Sales Order(sales module), then you can create profoma invoice(doesn't receive inv number yet) and a manager or admin can validate it. but invoice created from POS, is directly validated.

- you always have option to cancel an invoice in case you want to do some modification, you need to install Cancel Journal Items module, and enable canceling check box on the journal and then you can cancel an invoice, reset, modify and validate.(it would still assign same number).